Solve the following second-order linear homogeneous recurrence relations with constant coefficients.

a) an = −4an−1 − 4an−2 for all integers n ≥ 2 with a0 = 0, and a1 = −1.

b) an = an−1 + 6an−2 for all integers n ≥ 2 with a0 = 0, and a1 = 3.