Question

calculati 3+4+5+.......+30 =
15+16+17+......+70=
REZOLVARE + RASPUNS + VA ROG EXPLICAT

Answer 1

3 + 4 + 5 + ....... + 30 = 462

→ stabilesc cati termeni are suma cu ratia 1 ( 4 - 3 = 1;  5 - 4 = 1 .... )

30 - 3 + 1 = 27 + 1 = 28 termeni are suma

→ aplic formula sumei lui Gauss

= 28 × ( 3 + 30 ) / 2 =

= 14 × 33 =

= 462

__________________

15 + 16 + 17 + ..... + 70 = 2 380

70 - 15 + 1 = 56 de termeni are suma

= 56 × ( 15 + 70 ) / 2 =

= 28 × 85 =

= 2 380