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Question: Answered & Verified by Expert
Let y=yx be the solution of the differential equation, xdydx+y=xlogex, x>1. If 2y2=loge4-1, then ye is equal to
MathematicsDifferential EquationsJEE MainJEE Main 2019 (12 Jan Shift 1)
Options:
  • A -e2
  • B e4
  • C -e22
  • D e24
Solution:
2618 Upvotes Verified Answer
The correct answer is: e4

The given differential equation can be written as

dydx+yx=logex, which is a linear differential equation.

Now, integrating factor I.F.=e1xdx=elnx=x

Hence, the solution of the given differential equation is

y·x=x·logex dx

y·x=logexxdx-1xxdxdx (using integration by parts)

y·x=logexx22-1x·x22dx

y·x=logexx22-x2dx

xyx=x22logex-x24+C  ...1

Putting x=2 we get, 

2y2=2loge2-1+C

2y2=loge4-1+C

Given, 2y2=loge4-1

Then we get, C=0 

Now, from the equation 1 we get, 

yx=x2logex-x4

Putting x=e in above equation, we get,

ye=e2logee-e4=e2-e4=e4

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