Math Is Fun Forum

Mm... Thank you I do know about summation though, sorry about my rather obscure question.  What I was trying to say was that I forgot to specify that the limits are from r=0 to r=n at the beginning, that is:

I went through my algebra again and I just couldn't see how it gives 2^n (which is true for n is odd) *frown*...

Edited: I do know that it's just the summation of a row in the pascal triangle and I can prove it using the bionomial expression (x+y)^n where x = y = 1... I just can't make sense of the algebra and see how it gives 2^n