Question

Calculati suma S = { 3+6+9+ ... +2013}
Dau cel mai bun raspuns :)

Answer 1

S={3+6+9+...+2013}
S=3(1+2+3+...+671)
S=3x(671x672)/2
S=3x225456
S=676368
S=[nx(n+1)]/2
S=671x672/2
S=671x336
S=225456

Answer 2

In acest caz dam factor comun pe 3 de unde vom avea :
3(1+2+3+...+671)
In relatia din paranteza aplicam suma gauss si vom avea:3(671*672/2)=3*225456=676368