Question

Calculati suma
1+2+3+....+120



1+2+3+...+89

Answer 1

Folosim metoda lui Gauss (:primul termen+ultimul termen,inmultit cu cati termeni sunt,totul supra 2.)
1+2+3+....+120=$\frac{(1+120)* 120}{2}$=121*120:2=121*60=7260
1+2+3+....+89=$\frac{(1+89)*89}{2}$=89*90:2=89*45=4005