I'm having some problem recalling the trig identity.

I've work up till this part:

r^k . r^1 [Cos(k.theta)Cos(theta)-Sin(K.theta)Sin(theta)+i(Cos(theta)Sin(K.theta)+Co s(K.theta)Sin(theta)]

I need to reduce the above to its relevant trig identity to yield: r^(K+1) [Cos(K+1)theta + iSin(K+1)theta]

Solved: Thread to be delete