Question

Sa se rezolve !!! S= 2+4+6+ .......+80 .

Answer 1

S=2+4+6+...+80
S=2×(1+2+3+...+40)
S=2×(40×41:2)
S=2×(1640:2)
S=2×820
S=1640

Answer 2

S = 2 + 4 + 6+... + 80 → il dau factor comun pe 2
S = 2 × ( 1 + 2 + 3 +... + 40) → dublul sumei celor 40 de numere consecutive
S = 2 × [ 40 × (1 + 40) ] : 2 → aplic formula sumei lui Gauss
S = 40 × 41
S = 1 640