Prove Theorem $4:$ Let $c_{1},c_{2},\dots,c_{k}$ be real numbers. Suppose that the characteristic equation
$$r^{k}-c_{1}r^{k-1}-\dots c_{k} = 0$$
has $t$ distinct roots $r_{1},r_{2},\dots,r_{t}$ with multiplicities $m_{1},m_{2},\dots,m_{t},$ respectively, so that $m_{i}\geq 1\:\text{for}\: i = 1,2,\dots,t$ and $m_{1} + m_{2} + \dots + m_{t} = k.$ Then a sequence $\{a_{n}\}$ is a solution of the recurrence relation.
$$a_{n} = c_{1}a_{n-1} + c_{2}a_{n-2} + \dots + c_{k}a_{n-k}$$
if and only if
$$a_{n} = (\alpha_{1},0 + \alpha_{1,1n} + \dots + \alpha_{1,m_{1}-1}n^{m_{1}-1})r_{1}^{n} + (\alpha_{1},0 + \alpha_{2,1}n \dots \alpha_{1,m_{2}-1}n^{m_{2}-1})r_{2}^{n} +\dots + (\alpha_{t},0 + \alpha_{t,1}n \dots \alpha_{t,m_{t}-1}n^{m_{t}-1})r_{t}^{n} $$
for $n = 0, 1, 2,\dots,$ where $\alpha_{i,j}$ are constants for $1 \leq i \leq t\:\text{and}\: 0 \leq j \leq m_{i} - 1.$
