Jawaharlal Nehru Technological University

Jawaharlal Nehru Technological University B.Tech I MATHEMATICS-I Previous Question Paper (December - 2017 - R16)

B.Tech | I | I-I | R16 | December - 2017

Answer PaperPaper Code: 131AAMaximum Marks: 75Time: 3 hours

Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.

Part A

1a

Define exact differential equation. Give an example.

2 marks

Answer

A differential equation of the form M(x, y)dx + N(x, y)dy = 0 is said to be exact if there exists a function f(x, y) such that df = Mdx + Ndy. This condition is satisfied if and only if the partial derivatives satisfy the equality ∂M/∂y = ∂N/∂x.

An example of an exact differential equation is:

2xydx + (x2 + 1)dy = 0

Here, M = 2xy and N = x2 + 1. Since ∂M/∂y = 2x and ∂N/∂x = 2x, the equation is exact.

1b

Find a particular integral of

y'' - 2y' + y = x e^x

3 marks

Answer

The given differential equation is

f(D)y = (D2 - 2D + 1)y = x ex
where
D = d/dx
. The operator can be written as
(D - 1)2y = x ex
. The particular integral (PI) is given by
PI = 1/(D - 1)2 * (x ex)
. Using the exponential shift rule
1/f(D) * (eax V) = eax * 1/f(D + a) * V
, we set
a = 1
:
PI = ex * 1/((D + 1) - 1)2 * x = ex * 1/D2 * x
. Integrating
x
twice with respect to
x
gives
x3/6
. Thus, the particular integral is
PI = (x3 ex)/6
.
1c

Show that the matrix

A = [[3, 2+i], [i, -i]]
is Skew-Hermitian.

2 marks

Answer

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1d

Find the values of a and b such that the system x + 2y + 3z = 5, 2x + 7y + 3z = 9, 3x + y + az = b has no solution.

3 marks

Answer

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1e

Find the sum and product of the Eigen values of the matrix

A = [[1, 4, 6], [2, 2, 3], [-5, 7, 2]]
.

2 marks

Answer

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1f

Write the quadratic form corresponding to the matrix

A = [[1, 5, 7], [5, 4, 6], [7, 6, 3]]
.

3 marks

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1g

If u = f(x-y, y-z, z-x), find

∂u/∂x + ∂u/∂y + ∂u/∂z
.

2 marks

Answer

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1h

Expand f(x,y) = e^xy about origin up to 2nd degree terms.

3 marks

Answer

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1i

Form a partial differential equation by eliminating the arbitrary function f from z = f(x^2 + y^2).

2 marks

Answer

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1j

Solve p + q = 1.

3 marks

Answer

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Part B

210 marks
a

Solve (xy^2 - 2x^2y)dx + (3x^2y - x^3)dy = 0.

5 marks

Answer

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b

Solve y'' + y = sin x.

5 marks

Answer

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OR
310 marks
a

Apply the method of variation of parameters to solve y'' - y = x^2.

5 marks

Answer

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b

If the temperature of the air is 30°C and the substance cools from 100°C to 70°C in 15 minutes, find when the temperature will be 40°C.

5 marks

Answer

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410 marks
a

Find the rank of the matrix by reducing to echelon form: [[0, 1, 3, 1], [0, 0, 1, 1], [3, 1, 0, 2], [1, 1, 2, 0]].

5 marks

Answer

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b

Show that the system of equations 5x+3y+7z=4, 3x+26y+2z=9, 7x+2y+10z=5 is consistent and solve it.

5 marks

Answer

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OR
5

Solve the system of equations 2x-y+3z=4, x+y+z=1, x-3y-z=5 by LU – decomposition method.

10 marks

Answer

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610 marks
a

Find the Eigen values of A^5 - 2A^3 - A^2 - I if A = [[3, 7, 5], [2, 4, 3], [1, 2, 2]].

5 marks

Answer

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b

Using Cayley-Hamilton theorem, find A^-1 and A^-2 if A = [[4, 6, 6], [1, 3, 2], [-1, -4, -3]].

5 marks

Answer

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OR
7

Reduce the quadratic form Q = 2x^2 + 2y^2 + 2z^2 + 8xy + 7xz + 3yz to canonical form and hence find its rank, nature, index and signature.

10 marks

Answer

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810 marks
a

If f(x,y) = x^4+y^4 / x+y, show that x(∂f/∂x) + y(∂f/∂y) = 3f.

5 marks

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b

Determine whether the functions u = x+y/x-y, v = xy/x-y are dependent. If so, find the relation between them.

5 marks

Answer

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OR
910 marks
a

Find the Taylor series expansion of f(x,y) = e^x cos y in powers of (x-1) and (y - π/4).

5 marks

Answer

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b

Find the maximum and minimum values of the function f(x,y) = x^4 + y^4 - 2x^2 + 4xy - 2y^2 + 1.

5 marks

Answer

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1010 marks
a

Find all possible second order partial differential equations by eliminating the arbitrary constants a, b, c from x^2/a^2 + y^2/b^2 + z^2/c^2 = 1.

5 marks

Answer

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b

Solve (p-q)z = x + y.

5 marks

Answer

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OR
1110 marks
a

Reduce the equation p^2 + q^2 = z^2(px + qy) to F(p,q,z)=0 form and hence solve it.

5 marks

Answer

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b

Solve p^2y + q^2x = 1.

5 marks

Answer

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This page contains the question paper of MATHEMATICS-I from Jawaharlal Nehru Technological University for B.Tech AE I I-I, December - 2017, R16.

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