Question

Exercițiul 4. Aflați nr natural n, n >sau= 1

Answer 1

A de n luate cate  1 + C de n luate cate  2  ai formule = n!/(n-1)! + n!/2!(n-2)!

n(n-1)!/ (n-1)! + n(n-1)(n-2)!/2(n-2)!= faci simplificariille  n+n(n+1)/2=10  inmultesti cu 2  totul

2n+n(n+1)=20 deci 2n+n la a doua +n-20 =0

deci n la a doua +3n-20 =0  si acum rezolvi o ecuatie de graul 2