Question

решите уравнение Cn^2 = 28 (это сочетания из n по 2)

Answer 1

$C_{n}^{2} =28\\\\\frac{n!}{2!*(n-2)!}=28\\\\\frac{(n-2)!*(n-1)*n}{1*2*(n-2)!}=28\\\\n(n-1)=56\\\\n^{2}-n-56=0\\\\n_{1} =8\\\\n_{2} =-7<0-neyd\\\\Otvet:\boxed{n=8}$