1. Suppose that f(x) = 6x + 2 cosx is differentiable and has an inverse and f(π/2) = 3π. Find (f-1)'(3π).
2. Suppose that f(x) = x+5/x-1 is differentiable and has an inverse for x>1 and f(2) = 7. Find (f-1)'(7).
3. Suppose that f(x) = x - π + cosx is differentiable and has an inverse for 0 < x < 2π and f(π) = -1. Find (f-1)'(-1).