Solve: (1) a_n = 3a_n-1 + 4 and a_0 = 2. (2) a_n = 4a_n-2 + 1 and a_0 = 1, a_1 = 2. (3) a_n = 4a_n-2 + 2^n and a_0 = 0, a_1 = 2. (4) a_n = a_n-3 + 4^n and a_0 = 1, a_1 = 4, a_2 = 16. a_n = a_n-1 + 2^n + 1 and a_0 = 0