I need to prove the following using the binomial theorem

(n,k) = (n-2,k) + 2(n-2,k-1) + (n-2,k-2)

n

The binomial theorem states (1+x)^n = Sum (n,k)x^k

k=0

I don't know where to start, any hints would be helpful! ... Also (n,k) = n Choose k incase my text isn't clear