Q16 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

Consider the function fx=tan-13x-23+2x, ∀x≥0. If gx is the inverse function of fx, then the value of g ′ π 4 is equal to

Correct answer: 26

Solution

fx=tan-1x-231+x.23=tan-1x-tan-123
⇒f'x=11+x2  ...  1
Now, g'fx=1f'x ∵ gfx=x}
Putting x=5, we get,
g'f5=1f'5⇒g'tan−135−23+25=111+52
⇒g'tan−11=26⇒g'π4=26

Hence, the correct answer is 26.

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