Write the function in the form f (x) = (x - k)q(x) + r for the given value of k, and demonstrate that f (k) = r.
1. f (x) = x3 − x2 − 10x + 7, k = 3
2. f (x) = x3 − 4x2 − 10x + 8, k = −2
3. f (x) = 15x4 + 10x3 − 6x2 + 14, k = −23