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Question: Answered & Verified by Expert
If y=yx is the solution of the differential equation xdydx+2y=xex,y1=0 then the local maximum value of the function zx=x2y(x)-ex,xR is
MathematicsDifferential EquationsJEE MainJEE Main 2022 (26 Jun Shift 2)
Options:
  • A 1-e
  • B 0
  • C 12
  • D 4e-e
Solution:
1943 Upvotes Verified Answer
The correct answer is: 4e-e

Given,

dydx+2yx=ex

I.F.=e2xdx=e2lnx=x2

General solution: yx2=exx2dx

We know that

exfxdx==exfx-f'(x)+f''x-f'''x++-1nfnx+C

So, yx2=exx2-2x+2+C      ...i

Given y1=001=e11-21+2+C

C=-e

y=exx2x2-2x+2-e     (from eq i)

Hence, z(x)=x2exx2x2-2x+2-e-ex

=exx2-2x+2-e-ex 

zx=exx2-2x+1-e

z'x=ex2x-2+x2-2x+1ex

z'x=exx2-1
To find local maxima, put z'x=0

exx2-1=0   x-1x+1=0    ex>0, xR

x=1,-1

It is clear from the sign scheme method, zx has local maximum value at x=-1 and has local minimum value at x=1.

  The local maximum value is

z-1=e-1-12-2-1+1-e

=1e1+2+1-e =4e-e

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