For x ∈ R , x ≠ 0 , if y x is a differentiable function such that x ∫ 1 x y t d t = x + 1 ∫ 1 x t y t d t ,…

For xR, x0, if yx is a differentiable function such that x1xytdt=x+1 1xtytdt, then yx equals (where C is a constant)
  1. Cx3 e1x
  2. Cx2 e-1x
  3. Cx e-1x
  4. Cx3 e-1x

Solution

x1xytdt=x1xtytdt+ 1xtytdt

Differentiate w.r.t. x

1xy(t)dt+xy(x)=1xty(t)dt+x[xy(x)]+xy(x)

1xy(t)dt=1xty(t)dt+x2y(x) 

Differentiate again w.r.t. x

y(x)=xy(x)+2x y(x)+x2y'(x) 

1-3xyx=x2y'x

y'xyx=1-3xx2

1ydydx=1-3xx2

Integrating on both sides

lny=-1x-3lnx+C

ln(yx3)=-1x+C

yx3= e-1x+C

y=e-1x+Cx3

y=Cx3e-1x

Asked in: JEE Main 2016 (10 Apr Online)

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