9+10+11+...+30; Suma lui Gaus

Răspuns :

S = 1 + 2 + ... + 30 - (1 + 2 + ... + 8)     S = 30×31÷2 - 8×9÷2     S = 465 - 36     S = 429

9+10+11+.....+30 n=30-9+1=22 termeni S=n(30+9)/2=22(30+9)/2=11x39=429 /-supra.... ...........