2 + 5 + 8 + 11 + ....... + 59 + 62 = 672
→ stabilim cati termeni are suma, cu ratia 3 ( 5 - 2 = 3; 11 - 8 = 3; 62 - 59 = 3)
( 62 - 2) : 3 + 1 = 60 : 3 + 1 = 20 + 1 = 21 termeni are suma
= 21 x ( 2 + 62 ) / 2 = → am aplicat formula sumei lui Gauss
= 21 x 64 / 2 =
= 21 x 32 =
= 672
