Question

Preciso de ajuda...C11,7 e Cn,2

Answer 1

$C(n,r)=\dfrac{n!}{r!(n-r)!}\\\\\\C(11,7)=\dfrac{11!}{7!(11-7)!}=\dfrac{11!}{7!4!}=\dfrac{11\cdot10\cdot9\cdot8}{4\cdot3\cdot2}=11\cdot10\cdot3=330\\\\\\C(n,2)=\dfrac{n!}{2!(n-2)!}=\dfrac{n(n-1)(n-2)!}{2!(n-2)!}=\dfrac{n(n-1)}{2!}=\dfrac{n^2-n}{2}$