# Calculus Inverse function Derivative problem

## Homework Statement

f is a function with an inverse and it is differentiable. Use f(f-1(x))=x
and come up with the formula for the derivative of f-1

## The Attempt at a Solution

I tried expanding that equation to f'(f-1(x))*f'-1(x) -x
but I tested this and it didn't work.

Thanks

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vela
Staff Emeritus
Homework Helper
You started with an equation, and then you ended up without one. Could you describe what you did more carefully?

## Homework Statement

f is a function with an inverse and it is differentiable. Use f(f-1(x))=x
and come up with the formula for the derivative of f-1

## The Attempt at a Solution

I tried expanding that equation to f'(f-1(x))*f'-1(x) -x
but I tested this and it didn't work.

Thanks
You should just take the derivative of both sides. Use the chain rule on the left hand side.... Where did your equality go, and where did the -x come from?

use implicit differentiation