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## Homework Statement

Suppose f(x) is continuous and decreasing on the closed interval 5 <= x < 13, that f(5) = 9, f(13) = 5 and that the

integral of f(x) from 5 to 13 is 70.64758.

Then the integral of f^-1(x) from 5 to 9 is equal to what?

(Note: f^-1(x) is the inverse of f(x))

## Homework Equations

## The Attempt at a Solution

I really don't know how to solve this problem. I know that f^-1(f(x)) = x. Any ideas would be great. Thanks.