Question Number 23644 by Tinkutara last updated on 03/Nov/17
$${Prove}\:{that}\:\underset{{r}=\mathrm{0}} {\overset{{n}} {\sum}}{r}.^{{n}} {C}_{{r}} \:{z}^{{r}} \:=\:{nz}\left(\mathrm{1}\:+\:{z}\right)^{{n}−\mathrm{1}} \\ $$
Prove-that-r-0-n-r-n-C-r-z-r-nz-1-z-n-1-