Inverse Function Theorem in the text says:
If f is a differentiable function that is one-to-one near a and f'(a) ≠ 0, then
1. f^(-1)(x) is defined for x near b = f(a).
2. f^(-1)(x) is differentiable near b = f(a).
3. And last, but not least: f^(-1)'(b) = 1 / f'(a) where b = f(a).
Explain why f^(-1)'(x) involves f'(a) instead of f'(b). Also explain why the condition f'(a) ≠ 0 is necessary: