we have that
3 = 3 + 0i -----------> rewrite as 3(1 + 0i)
So now what we have to do is figure out which of the above expressions has cos a = 1 and sin a = 0.
cos 0 = 1, and sin 0 = 0, so that's the answer that we want.
the answer is:
3 = 3(cos 0 + i sin 0)
