FINDING INVERSE OF A FUNCTION IS NOT ALWAYS EASY

Calculus Level pending

Let f ( x ) = x 3 + e x 2 f(x)= x^3 + e^{\frac{x}{2}} and g ( x ) = f 1 ( x ) g(x)=f^{-1}(x) then find g ( 1 ) g'(1)


The answer is 2.

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2 solutions

Himanshu Arora
Jun 29, 2014

Inverse functions look symmetric about x=y on the graph. So for finding g ( 1 ) g'(1) what we can do is find (\f'(x)) at the point where it is equal to 1 and then take reciprocal of it. See it from the graph if it is hard to comprehend just by reading.

Now one solution that clearly strikes for f ( x ) = 1 f(x)=1 is x=0 and then we are done. Answer: 2 \boxed{2} Cheers

Naveen Verma
May 14, 2014

Since g(x) is inverse if f(x) g(f(x))=x

Diff wrt x g'(f(x))*f'(x)=1

Now f(0)=1 and f'(0)=.5 So g'(1)=1/f'(0)=2

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