## Algebra 2 (1st Edition)

We know that $_nC_r=\frac{n!}{r!(n-r)!}$. Hence $_nC_r=\frac{n!}{r!(n-r)!}=\frac{n!}{(n-r)!r!}=\frac{n!}{(n-r)!(n-(n-r))!}=_nC_{n-r}$ Thus we proved what we had to.