I need help with the following problem.

> 
> $a\_0=1$
> 
> 
> $a\_1=-3$
> 
> 
> $a\_n=-2\*a\_{n-1}+3\*a\_{n-2}$, for all $n\ge2$
> 
> 
> prove $a\_n=(-3)^n$
> 
> 
> 

I understand the base cases, I'm just confused on how to do the strong induction step. I know that we are showing that if P(n) is true then it must hold for P(n+1) but I don't know how to do that with $a\_{n+1}$