I've got a question I'm really not sure how to do. here it is:

Consider the following difference equation:

q(n) = 2*q(n-1) + q(n-2) - 2*q(n-3)

Let q(n) = ar^n. Show that r must satisfy (r-1)(r+1)(r-2) = 0

It doesnt look to hard, im just not quiet sure exactly how to go about it...