Q30 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

Consider a function fx=xx, ∀x∈1,∞. If gx is the inverse function of fx, then the value of g ′ 4 is equal to

  • A
    log2⁡e
  • B
    12log2e⁡e
  • Correct answer
    C
    14log2e⁡e
  • D
    12loge⁡2e

Solution

fx=xx⇒log⁡fx=xlog⁡x
Differentiating with respect to x, we get,

  f ′ x = x x 1+logx
Now, by property g ′ f x = 1 f ′ x {∵gx is the inverse of fx}
Putting x=2
g'f2=1f'2⇒g'4=1221+log2=14log2ee

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

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