[University Math] How to prove there are two distinct points where f'(x)=1?
I am trying to solve the following problem:
Let f be a differentiable function on [0,1] such that f(0)=0 and f(1)=1. Prove that there exist two distinct numbers a,b in (0,1) such that
f'(a)f'(b)=1
By the Mean Value Theorem, I know that there exists some c in (0,1) such that
f'(c)=1
since
(f(1)-f(0))/(1-0)=1
But I do not know how to prove that there exists another point d different from c in (0,1) such that
f'(d)=1
Any hints or ideas?