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NCERT Solutions for class 12 Maths | Chapter 9 - Differential Equations

(1) The solution of is
[A]
[B] xex + cx
[C] y = xex + k
[D]
Answer:
(2) The differential equation of the family of cuves x² + y² – 2ay = 0, where a is arbitrary constant is
[A] (x² – y²)dy/dx = 2xy
[B] 2 (x² + y²)dy/dx = xy
[C] 2(x² – y²)dy/dx = xy
[D] (x² + y²) dy/dx = 2xy
Answer: (x² – y²)dy/dx = 2xy

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(3) The solution of dy/dx + y = e-x, y (0) = 0 is
[A] y = e-x (x – 1)
[B] y = xex
[C] y = xe-x + 1
[D] y = xe-x
Answer: y = xe-x
(4) The order and degree of the differential equation

[A] 1, 3/2
[B] 2, 3
[C] 2, 1
[D] 3, 4
Answer: 2, 1
(5) Which of the following is the general solution of
[A] y = (Ax + B)ex
[B] y = (Ax + B)e-x
[C] y = Aex + Be-x
[D] y = A cos x + B sin x
Answer: y = (Ax + B)ex
(6) The integrating factor of the differential equation is
[A] xe/x
[B] ex/x
[C] xex
[D] ex
Answer: ex/x
(7) Solution of dy/dx – y = 1 y(0) = 1 is given by
[A] xy = -ex
[B] xy = -e-x
[C] xy = -1
[D] y = 2ex – 1
Answer: y = 2ex – 1
(8) Solution of the differential equation tan y sec² x dx + tan x sec² y dy + 0 is .
[A] tan x + tan y = k
[B] tan x – tan y = k
[C] tanx/tany = k
[D] tan x.tan y = k
Answer: tan x.tan y = k
(9) The order and degree of the differential equation

[A] 1, 4
[B] 3, 4
[C] 2, 4
[D] 3, 2
Answer: 3, 2
(10) The general solution of dy/dx = 2x ex2-y is
[A] ex2-y = c
[B] e-y + ex2  = c
[C] ey = ex2  + c
[D] ex2+y = c
Answer: ey = ex2  + c
(11) y = aemx + be-mx satisfies which of the following differential equation?
[A] dy/dx + my = 0
[B] dy/dx – my = 0
[C] d2y/dx2 – m²y = 0
[D] d2y/dx2 +m²y = 0
Answer: d2y/dx2 – m²y = 0
(12) The solution of the equation (2y – 1) dx-(2x + 3)dy = 0 is
[A]
[B]
[C]
[D]
Answer:
(13) Integrating factor of xdy/dx – y = x4 – 3x is
[A] x
[B] log x
[C] 1/2
[D] -x
Answer: 1/2
(14) The differential equation for which y = a cos x + b sin x is a solution is
[A]
[B]
[C]
[D]
Answer:
(15) The solution of dy/dx + y = e-x, y (0) = 0 is
[A] y = ex(x – 1)
[B] y = xe-x
[C] y = xe-x + 1
[D] y = (x + 1 )e-x
Answer: y = xe-x
(16) If y dx + y2 dy = x dy, x ∈ R, y > 0 and y(1) = 1, then y(-3) =
[A] 3
[B] 2
[C] 1
[D] 5
Answer: 3
(17) The differential equation determines a family of circle with
[A] variable radii and fixed centre (0, 1)
[B] variable radii and fixed centre (0, -1)
[C] fixed radius 1 and variable centre on x-axis
[D] fixed radius 1 and variable centre on y-axis
Answer: fixed radius 1 and variable centre on x-axis
(18) The particular solution In(dy/dx) = 3x + 4y, y(0) = 0 is
[A] e3x + 3e-4y = 4
[B] 4e3x – 3e-4y = 3
[C] 3e3x + 4e4y = 7
[D] 4e3x + 3e-4y = 7
Answer: 4e3x + 3e-4y = 7
(19) The solution of differential equation dy/dx=x−y/x+y is
[A] x2 – y2 + 2xy + c = 0
[B] x2 – y2 – xy + c = 0
[C] x2 – y2 + xy + c = 0
[D] x2 – y2 – 2xy + c = 0
Answer: x2 – y2 – 2xy + c = 0
(20) The solution of the differential equation x dy + (x + y) dx = 0 is
[A]
[B]
[C]
[D] None of these
Answer:

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