Răspuns :
[tex]2+4+6+...+60= \\ \\ 2*(1+2+3+...+30)= \\ \\ 2*(30*31:2)= \\ \\ 2*465=930[/tex]
[tex]2 + 4 + 6 + ..... + 60 = \\ = 2 \times (1 + 2 + 3 + ... + 30) \\ = 2 \times (30 \times 31 \div 2) \\ = 2 \times 465 \\ = 930[/tex]