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.... ...........
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.... ...........