# Binomial Theorem

Hello,

All we know the Binomial Theorm which may be stated mathematically as:

$$\left(x+y\right)^n=\sum_{k=0}^n{n\choose k}y^k\,x^{n-k}$$

Now suppose that we have the following mathematical expression:

$$\sum_{k=0}^{n}{n\choose k}\,(-1)^k$$

if we substitute x=1 and y=-1 in the first equation we get the second. Is that mean the second equation is essentially zero, since $$(1-1)^n=0$$??

Regards