I have a small algebra problem that i hope anyone can help me with. I have this example in my textbook that have this step i don't follow.
y_n-y_(n-1)-2y_(n-2) = 0 where n = 3,4,5,...
y_1 = 1
y_2 = 3
with y_n = x^n
And what i don't understand is how they get this that to this: