Q90 / 150 · MHT CET 2019 (Shift 2) · Mathematics

If then xy=ex-y, then dydx at x =1 is ….

  • A
    e
  • B
    1
  • Correct answer
    C
    0
  • D
    -1

Solution

Given have, xy=ex-y
taking log on both sides, we get
ylogx=x-yloge=x-y ….(i)
when x=1,thenylog1=1-y
⇒y=1
On differentiating both sides,
y1x+logx.dydx=1-dydx
⇒dydxlogx+1=1-yx
⇒dydxlogx+1=x-yx
⇒dydx=x-yxlogx+1
when x = 1, then
dydx=1-11log1+1=0

Hence, the correct answer is option: 'C'.

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