I have the following problem to solve:

a_n = 4a_{n-1} - 4a_{n-2}

where a_0 = -5 and a_1 = 3

which I have attempted to solve via substitution, ie a_n = r^n

When I do this, I end up with the result (r-2)^2 = 0

hence, r = 2.

When I put this back into the equation, I then get

A + B = -5

2A + 2B = 2(A + B) = 3

=> 0 = 13.

What am I fumbling in here??