metoda 1:
delta=(-11)^2-4*(-26)*1=121+104=225
n=(11+-radical din 225)/2
n=(11+-15)/2
n1=(11+15)/2=26/2=13
n2=(11-15)/2=-4/2=-2
metoda 2:
n^2-13n+2n-26=0
n(n-13)+2(n-13)=0
(n-13)(n+2)=0
n-13=0 => n=13 sau n+2=0 => n=-2
