Question

Calculati urmatoarele sume:
a)S=2+4+6+...1000
b)S=3+6+9+...+2013
c)S=5+10+15+500
d)S=7+14+21+...+700
Raspuns urgent!!
Dau coroana

Answer 1

a) 2 + 4 + 6 +... + 1000 = 2(1 + 2 +3 +... +500) = 2 * 500 * 501 : 2 =
    2 * 250 * 501 = 250500
b) 3 + 6 + 9 +.... + 2013 = 3(1 + 2 + 3 +... + 671) = 3 * 671 * 672 : 2 = 
    3 * 671 * 336 = 676368
c) 5 + 10 + 15 + ... + 500 = 5 (1 + 2 + 3 + ... + 100) = 5 * 100 * 101 : 2 =
    5 * 101 * 50 = 25250
d) 7 + 14 + 21 + ... + 700 = 7 (1 + 2 + 3 + ... + 100) = 7 * 100 * 101 : 2 = 
    7 * 50 * 101 = 35350