Q32 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

If xy.yx=16, then the value of dydx at (2, 2) is

  • Correct answer
    A
    -1
  • B
    0
  • C
    1
  • D
    None of these

Solution

Since, xy.yx=16

∴loge⁡xy+loge⁡yx=loge⁡16

⇒yloge⁡x+xloge⁡y=4loge⁡2

Now, on differentiating both sides w.r.t. x, we get

yx+loge⁡xdydx+xydydx+loge⁡y.1=0

⇒dydx=-loge⁡y+yxloge⁡x+xy

∴dydx(2,2)=-(loge⁡2+1)(loge⁡2+1)=-1

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

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