Apply the method of Exercise 9.1.21 to solve the following iterative equations:
(a) $u^{(k+2)}=-u^{(k+1)}+2 u^{(k)}, \quad u^{(0)}=1, \quad u^{(1)}=2$.
(b) $12 u^{(k+2)}=u^{(k+1)}+u^{(k)}, \quad u^{(0)}=-1, \quad u^{(1)}=2$.
(c) $u^{(k+2)}=4 u^{(k+1)}+u^{(k)}, \quad u^{(0)}=1, \quad u^{(1)}=-1$.
(d) $u^{(k+2)}=2 u^{(k+1)}-2 u^{(k)}, \quad u^{(0)}=1, \quad u^{(1)}=3$.
(e) $u^{(k+3)}=2 u^{(k+2)}+u^{(k+1)}-2 u^{(k)}, \quad u^{(0)}=0, \quad u^{(1)}=2, \quad u^{(2)}=3$.
(f) $u^{(k+3)}=u^{(k+2)}+2 u^{(k+1)}-2 u^{(k)}, \quad u^{(0)}=0, \quad u^{(1)}=1, \quad u^{(2)}=1$.