This problem considers several ways to compute xn for some n >= 0.
(a) Write an iterative function power1 to compute xn for n >= 0.
(b) Write a recursive function power2 to compute xn by using the following recursive formulation:
x0 = 1
xn = x * xn-1 if n > 0
(c) Write a recursive function power3 to compute xn by using the following recursive formulation:
x0 = 1
xn = (xn/2)2 if n > 0 and n is even
xn = x * (xn/2)2 if n > 0 and n is odd