Question

16. Calculaţi: a) 3 + 6 + 9 + 12 + ... +2 019; c) 5 + 10 + 15 + 20+ ... + 2 020;​

Answer 1

Răspuns:

A) 3+6+9+12+....+2 019

3*(1+2+3+...+673)=

=3*[(673+1)*673:2]=

=3*(674*673:2)=

=3*(453 602:2)

=3*226 801=

=680 403

c)5+10+15+20+....+2020=

5*(1+2+3+4+...+404)=

5*[(404+1)*404:2]=

5*(405*404:2)=

5*(163 620:2)=

5*81 810=

409 050