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Ramana Sri IAS - 2016 UPSC Maths Optional Paper I Solutions

2016 UPSC Maths Optional Paper I Solutions

Ramana Sri IAS provides complete and updated solutions for the 2016 UPSC Maths Optional Paper I. Aspirants preparing for the UPSC Mains Examination with Mathematics as their optional subject should solve all these questions carefully at least 5 to 10 times before the mains examination.

Ramana Sri IAS presents complete solutions for UPSC/IAS/CSE-Civil Service Examination 2016 Mathematics Optional Paper I. Each answer follows the same format: Question, Diagram where needed, Concept Related to the Question, Detailed Solution, and Final Answer.

About 2016 UPSC Maths Optional Paper I Solutions

These 2016 UPSC Maths Optional Paper I Solutions are prepared by Ramana Sri IAS for aspirants who want question-wise clarity before the UPSC Mains examination. This public page gives one full sample solution, while the complete paper-wise solutions are available in the full PYQ course.

Students can use these 2016 UPSC Maths Optional Paper I Solutions to understand the expected answer-writing method, diagram presentation, concept application, and final-answer format used by Ramana Sri IAS.

For the official examination source, students may also refer to the UPSC previous year question papers page.

These 2016 UPSC Maths Optional Paper I Solutions are useful for revision, answer-writing practice, and understanding the step-by-step method expected in the UPSC Mathematics optional paper.

Sample Full Solution

We are giving one question as a free sample solution below: Question 1(d). This free sample includes all five sections: Question, Diagram, Concept Related to the Question, Detailed Solution, and Final Answer. Complete solutions for all questions are available in the full PYQ course. To purchase the full solutions, please fill out the admission form first. Our Ramana Sri IAS admission team will guide you through WhatsApp, email, or call.

2016 UPSC Maths Optional Paper I Solutions: Table of Contents

Question 1(a)(i)

Inverse of a matrix by elementary row operations

1Question

Using elementary row operations, find the inverse of \(A={\large \left[\begin{smallmatrix}1&2&1\\1&3&2\\1&0&1\end{smallmatrix}\right]}\).

2Diagram

Full Solution Access

The Diagram section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

Full Solution Access

The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

Full Solution Access

The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

Full Solution Access

The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 1(a)(ii)

Finding \(A^{14}+3A-2I\)

1Question

If \(A={\large \left[\begin{smallmatrix}1&1&3\\5&2&6\\-2&-1&-3\end{smallmatrix}\right]}\), then find \(A^{14}+3A-2I\).

2Diagram

Full Solution Access

The Diagram section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

Full Solution Access

The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

Full Solution Access

The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

Full Solution Access

The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 1(b)(i)

Condition for consistency of linear equations

1Question

Using elementary row operations, find the condition that the linear equations \(x-2y+z=a\), \(2x+7y-3z=b\), \(3x+5y-2z=c\) have a solution.

2Diagram

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The Diagram section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

Full Solution Access

The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 1(b)(ii)

Dimensions of subspace intersection and sum

1Question

If \(W_1=\{(x,y,z)\mid x+y-z=0\}\), \(W_2=\{(x,y,z)\mid 3x+y-2z=0\}\), and \(W_3=\{(x,y,z)\mid x-7y+3z=0\}\), then find \(\dim(W_1\cap W_2\cap W_3)\) and \(\dim(W_1+W_2)\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 1(c)

Evaluation of an improper integral

1Question

Evaluate \(I=\int_0^1 \sqrt[3]{x\log\left(\frac{1}{x}\right)}\,dx\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 1(d)

Sphere through a given circle

1Question

Find the equation of the sphere which passes through the circle \(x^2+y^2=4,\ z=0\) and is cut by the plane \(x+2y+2z=0\) in a circle of radius \(3\).

2Diagram

Question 1(d): Sphere cut by a plane
2016 UPSC Maths Optional Paper I Solutions diagram for Question 1(d), showing the sphere through the circle x squared plus y squared equals 4 and the cutting plane forming a circle of radius 3.

3Concept Related to the Question

A family of spheres passing through a fixed circle is obtained by combining the equation of the sphere through the circle with the equation of the plane of the circle. Then the radius of the circular section made by a plane is found from \(r^2=R^2-d^2\), where \(R\) is the sphere radius and \(d\) is the distance of the centre from the cutting plane.

4Detailed Solution

The circle is given by

\[ x^2+y^2=4,\qquad z=0. \]

Every sphere passing through this circle can be written as

\[ x^2+y^2+z^2+\lambda z-4=0. \]

This is because putting \(z=0\) gives \(x^2+y^2-4=0\), which is exactly the given circle. Now complete the square in \(z\):

\[ x^2+y^2+\left(z+\frac{\lambda}{2}\right)^2=4+\frac{\lambda^2}{4}. \]

Hence the centre is \(C=(0,0,-\lambda/2)\), and

\[ R^2=4+\frac{\lambda^2}{4}. \]

The distance of \(C\) from the plane \(x+2y+2z=0\) is

\[ d=\frac{|0+0+2(-\lambda/2)|}{\sqrt{1^2+2^2+2^2}}=\frac{|\lambda|}{3}. \]

The plane cuts the sphere in a circle of radius \(3\). Therefore

\[ 3^2=R^2-d^2=4+\frac{\lambda^2}{4}-\frac{\lambda^2}{9}. \]

So

\[ 9=4+\frac{5\lambda^2}{36}\quad\Rightarrow\quad \lambda^2=36. \]

Thus \(\lambda=\pm6\).

5Final Answer

The required spheres are \(x^2+y^2+z^2+6z-4=0\) and \(x^2+y^2+z^2-6z-4=0\).

Question 1(e)

Shortest distance between two lines

1Question

Find the shortest distance between the lines \(\frac{x-1}{2}=\frac{y-2}{4}=z-3\) and \(y-mx=z=0\). For what value of \(m\) will the two lines intersect?

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 2(a)(i)

Matrix representation and null space of a linear transformation

1Question

If \(M_2(R)\) is space of real matrices of order \(2\times2\) and \(P_2(x)\) is the space of real polynomials of degree at most \(2\), then find the matrix representation of \(T:M_2(R)\to P_2(x)\), such that \(T\!\left({\large \left[\begin{smallmatrix}a&b\\c&d\end{smallmatrix}\right]}\right)=a+c+(a-d)x+(b+c)x^2\), with respect to the standard bases of \(M_2(R)\) and \(P_2(x)\). Further find the null space of \(T\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 2(a)(ii)

Matrix of a polynomial transformation

1Question

If \(T:P_2(x)\to P_3(x)\) is such that \(T(f(x))=f(x)+5\int_0^x f(t)\,dt\), then choosing \(\{1,1+x,1-x^2\}\) and \(\{1,x,x^2,x^3\}\) as bases of \(P_2(x)\) and \(P_3(x)\) respectively, find the matrix of \(T\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 2(b)(i)

Eigenvalues and eigenvectors

1Question

If \(A={\large \left[\begin{smallmatrix}1&1&0\\1&1&0\\0&0&1\end{smallmatrix}\right]}\), then find the eigenvalues and eigenvectors of \(A\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 2(b)(ii)

Eigenvalues of a Hermitian matrix are real

1Question

Prove that eigenvalues of a Hermitian matrix are all real.

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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The Final Answer section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 2(c)

Finding a linear transformation from its matrix representation

1Question

If \(A={\large \left[\begin{smallmatrix}1&-1&2\\-2&1&-1\\1&2&3\end{smallmatrix}\right]}\) is the matrix representation of a linear transformation \(T:P_2(x)\to P_2(x)\) with respect to the bases \(\{1-x,x(1-x),x(1+x)\}\) and \(\{1,1+x,1+x^2\}\), find \(T\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 3(a)

Maximum and minimum under two constraints

1Question

Find the maximum and minimum values of \(x^2+y^2+z^2\) subject to the conditions \(\frac{x^2}{4}+\frac{y^2}{5}+\frac{z^2}{25}=1\) and \(x+y-z=0\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 3(b)

Delta condition near the origin

1Question

Let

\[ f(x,y)= \begin{array}{ll} \dfrac{2x^4y-5x^2y^2+y^5}{(x^2+y^2)^2}, & (x,y)\ne(0,0),\\[6pt] 0, & (x,y)=(0,0). \end{array} \]

Find \(\delta>0\) such that \(|f(x,y)-f(0,0)|<.01\), whenever \(\sqrt{x^2+y^2}<\delta\).

2Diagram

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The Diagram section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 3(c)

Surface area cut from a plane

1Question

Find the surface area of the plane \(x+2y+2z=12\) cut off by \(x=0\), \(y=0\), and \(x^2+y^2=16\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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The Concept Related to the Question section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 4(a)

Surface generated by a moving line

1Question

Find the surface generated by a line which intersects the lines \(y=a=z\), \(x+3z=a=y+z\) and parallel to the plane \(x+y=0\).

2Diagram

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

3Concept Related to the Question

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 4(b)

Mutually perpendicular generators of a cone

1Question

Show that the cone \(3yz-2zx-2xy=0\) has an infinite set of three mutually perpendicular generators. If \(\frac{x}{1}=\frac{y}{1}=\frac{z}{2}\) is a generator belonging to one such set, find the other two.

2Diagram

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3Concept Related to the Question

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

4Detailed Solution

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 4(c)

Double integral over a rectangle

1Question

Evaluate \(\displaystyle \iint_R f(x,y)\,dx\,dy\) over the rectangle \(R=[0,1;0,1]\) where

\[ f(x,y)= \begin{array}{ll} x+y, & x^2\lt y\lt 2x^2,\\[4pt] 0, & \text{elsewhere.} \end{array} \]

2Diagram

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3Concept Related to the Question

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4Detailed Solution

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Question 4(d)

Locus of intersection of three mutually perpendicular tangent planes

1Question

Find the locus of the point of intersection of three mutually perpendicular tangent planes to the conicoid \(ax^2+by^2+cz^2=1\).

2Diagram

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3Concept Related to the Question

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4Detailed Solution

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The Detailed Solution section for this question is available in the full 2016 UPSC Maths Optional Paper I PYQ Solutions course.

Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 5(a)

Particular integral

1Question

Find a particular integral of \(\dfrac{d^2y}{dx^2}+y=e^{\dfrac{x}{2}}\sin\dfrac{\sqrt3x}{2}\).

2Diagram

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3Concept Related to the Question

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4Detailed Solution

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

Question 5(b)

Triangle sides and medians

1Question

Prove that the vectors \(\vec a=3\hat i+\hat j-2\hat k\), \(\vec b=-\hat i+3\hat j+4\hat k\), and \(\vec c=4\hat i-2\hat j-6\hat k\) can form the sides of a triangle. Find the lengths of the medians of the triangle.

2Diagram

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3Concept Related to the Question

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4Detailed Solution

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Complete diagrams, concepts, detailed solutions and final answers for all questions are available in the full PYQ course.

5Final Answer

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Question 5(c)

First-order differential equation

1Question

Solve \(\dfrac{dy}{dx}=\dfrac{1}{1+x^2}\left(e^{\tan^{-1}x}-y\right)\).

2Diagram

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Question 5(d)

Self-orthogonal family of parabolas

1Question

Show that the family of parabolas \(y^2=4cx+4c^2\) is self-orthogonal.

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Question 5(e)

Path under inverse-cube central acceleration

1Question

A particle moves with a central acceleration which varies inversely as the cube of the distance. If it is projected from an apse at a distance \(a\) from the origin with a velocity which is \(\sqrt2\) times the velocity for a circle of radius \(a\), then find the equation to the path.

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Question 6(a)

Solving a first-order differential equation

1Question

Solve \(\{y(1-x\tan x)+x^2\cos x\}\,dx-x\,dy=0\).

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Question 6(b)

Variation of parameters

1Question

Using the method of variation of parameters, solve the differential equation \((D^2+2D+1)y=e^{-x}\log(x)\), \(\left[D=\frac{d}{dx}\right]\).

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Question 6(c)

Cauchy-Euler differential equation

1Question

Find the general solution of \(x^2\dfrac{d^3y}{dx^3}-4x\dfrac{d^2y}{dx^2}+6\dfrac{dy}{dx}=4\).

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Question 6(d)

Solution by Laplace transformation

1Question

Using Laplace transformation, solve \(y''-2y'-8y=0\), \(y(0)=3\), \(y'(0)=6\).

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Question 7(a)

Reaction at the hinge of a rod

1Question

A uniform rod \(AB\) of length \(2a\) movable about a hinge at \(A\) rests with other end against a smooth vertical wall. If \(\alpha\) is the inclination of the rod to the vertical, prove that the magnitude of reaction of the hinge is \(\frac{1}{2}W\sqrt{4+\tan^2\alpha}\), where \(W\) is the weight of the rod.

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Question 7(b)

Inclination of a light rod kept apart by strings

1Question

Two weights \(P\) and \(Q\) are suspended from a fixed point \(O\) by strings \(OA\), \(OB\) and are kept apart by light rod \(AB\). If the strings \(OA\) and \(OB\) make angles \(\alpha\) and \(\beta\) with the rod \(AB\), show that the angle \(\theta\) which the rod makes with the vertical is given by

\[ \tan\theta=\dfrac{P+Q}{P\cot\alpha-Q\cot\beta}. \]

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Question 7(c)

Tension in an endless string passing over square pegs

1Question

A square \(ABCD\), the length of whose sides is \(a\), is fixed in a vertical plane with two of its sides horizontal. An endless string of length \(l(>4a)\) passes over four pegs at the angles of the board and through a ring of weight \(W\) which is hanging vertically. Show that the tension of the string is \(\dfrac{W(l-3a)}{2\sqrt{l^2-6la+8a^2}}\).

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Question 8(a)

Finding a scalar function from its gradient

1Question

Find \(f(r)\) such that \(\nabla f=\dfrac{\vec r}{r^5}\) and \(f(1)=0\).

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Question 8(b)

Vector integral identity

1Question

Prove that \(\oint_C f\,d\vec r=\iint_S d\vec S\times\nabla f\).

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Question 8(c)

Time of arrival under variable acceleration

1Question

A particle moves in a straight line. Its acceleration is directed towards a fixed point \(O\) in the line and is always equal to \(\mu\left(\frac{a^5}{x^2}\right)^{\frac{1}{3}}\) when it is at a distance \(x\) from \(O\). It starts from rest at distance \(a\) from \(O\), then find the time, the particle will arrive at \(O\).

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Question 8(d)

Radius of curvature of a cardioid

1Question

For the cardioid \(r=a(1+\cos\theta)\), show that the square of the radius of curvature at any point \((r,\theta)\) is proportional to \(r\). Also find the radius of curvature if \(\theta=0,\frac{\pi}{4},\frac{\pi}{2}\).

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2016 UPSC Maths Optional Paper I Solutions FAQs

Are these 2016 UPSC Maths Optional Paper I Solutions complete?

This public page gives one complete sample solution. Complete solutions for all questions are available in the full PYQ course.

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Question 1(d) is given as the free sample solution on this page.

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