1. The problem statement, all variables and given/known data 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)) 2. Relevant equations 3. 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.