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JEE Main 20204 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
4 September
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2020 · 4 September · Morning Shift · Mathematics · Differential Equations

Let y = y ( x ) be the solution of the differential equation, x y ^...

Let y=y(x)y = y ( x ) be the solution of the differential equation, xy′−y=x2(xcosx+sin⁡x)x{y}^{'} - y = {x}^{2} ( xcosx + \sin x ),x>0x > 0. If y(π)=π,y ( \pi ) = \pi, then y ' '\left(\dfrac{\pi}{2}\right) + y(π2)\left(\dfrac{\pi}{2}\right) is equal to :

Options

  1. A2+π22 + \dfrac{\pi}{2}
  2. B1+π2+π241 + \dfrac{\pi}{2} + \dfrac{{\pi}^{2}}{4}
  3. C2+π2+π242 + \dfrac{\pi}{2} + \dfrac{{\pi}^{2}}{4}
  4. D1+π21 + \dfrac{\pi}{2}

Correct answer

A. 2+π22 + \dfrac{\pi}{2}

Step-by-step solution

Given xdydx−y=x2(xcos+sin⁡x)x\dfrac{dy}{dx} - y = {x}^{2}\left(xcos + \sin x\right)

⇒⇒dydx−1xy=x(xcosx+sin⁡x)\dfrac{dy}{dx} - \dfrac{1}{x}y = x\left(xcosx + \sin x\right)

∴∴ I.F =e−ln⁡x=1x= {e}^{- \ln x} = \dfrac{1}{x}

∴∴ Solution is y.1x=∫1x.x(xcosx+sin⁡x)dxy . \dfrac{1}{x} = ∫ \dfrac{1}{x} . x\left(xcosx + \sin x\right)dx

yx=∫(xcosx+sin⁡x)dx\dfrac{y}{x} = ∫ \left(xcosx + \sin x\right)dx

yx=xsinx+C\dfrac{y}{x} = xsinx + C

∵y(π)=π⇒C=1∵ y\left(\pi\right) = \pi ⇒ C = 1

y=x2sin⁡x+xy = {x}^{2}\sin x + x

dydx=x2cos⁡x+2xsinx+1\dfrac{dy}{dx} = {x}^{2}\cos x + 2xsinx + 1

d2ydx2=−x2sin⁡x+2xcosx+2sin⁡x+2xcosx\dfrac{{d}^{2}y}{d{x}^{2}} = - {x}^{2}\sin x + 2xcosx + 2\sin x + 2xcosx

=−x2sin⁡x+4xcosx+2sin⁡x= - {x}^{2}\sin x + 4xcosx + 2\sin x

∴∴ y′′(π2)+y(π2)=(−π24+0+2)+(π24+π2){y}^{''}\left(\dfrac{\pi}{2}\right) + y\left(\dfrac{\pi}{2}\right) = \left(- \dfrac{{\pi}^{2}}{4} + 0 + 2\right) + \left(\dfrac{{\pi}^{2}}{4} + \dfrac{\pi}{2}\right)

=−π24+2+π24+π2= - \dfrac{{\pi}^{2}}{4} + 2 + \dfrac{{\pi}^{2}}{4} + \dfrac{\pi}{2}

=π2+2= \dfrac{\pi}{2} + 2.

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