Question

sa se calculeze sumele 1+3+5.....+71

Answer 1

(71×72):2=71×36=2 556
sau
=5 112:2=2 556

Answer 2

S1 = 1 + 3 + 5 + 71; S= 1 + 2 + 3 +4 +...+72; S2 = 2+ 4 + 6 + 8 +...+72; S = 72•73/2 = 2628; S2 = 2• (1 + 2 +3 +...+ 36) 2•36•37/2= 1332 => S1 =S - S2 = 2628 - 1332 = 1296 = (72/2)^2