Pn+2/Pn=12
(n+2)!/n!=10
n!*(n+1)(n+2)/n!=12
(n+1)(n+2)=12
n²+2n+n+2-12=0
n²+3n-10=0
n1=n2=-3 U n1*n2=-10
n1=-5 не удов усл
n2=2
ответ 4
