one of the questions on my homework is expressing below formula in terms of big Theta.
$f(n)=4f(n-1)+4f(n-2)$
clearly it looks linear homogeneous but when I try to start the solution by $x^2 - 4x - 4=0$, there is no factors.
we have another options to solve it either by expansion which is very costly and not logical or using change of variable which I couldn't do.
anyone has an idea your help is very appreciated.