Question

Calculați 3+6+9+...+33

Answer 1

S=3+6+9+...+33=3(1+2+3+....11)
suma Gauss cu formula de calcul S=[n(n+1)]:2

S=3×(11×12):2

S=198

Answer 2

3 + 6 + 9 + .... + 33

Folosim procedeul numit "Regula de recurenta".

3 = 3 x 1
6 = 3 x 2
......
33 = 3 x 11
---------------------- Adunare
S = 3 x (1 + 2 + 3 + ..... + 11)

1 + 2 + .... + 11 = 11 x 12 : 2 (Suma lui Gauss)
11 x 12 = 132
132 : 2 = 66

S = 3 x 66
S = 198

3 + 6 + 9 + ..... + 33 = 198