Question

1+13+25+...+121=? Ajutor nu stiu sa rezolv.PLS

Answer 1

[tex]S = 1 + 13 + 25 + ... + 121\\ S = (0 + 1) + (12 + 1) + (24 + 1) + ... + (120 + 1)\\ S = 12 + 24 + ... + 120 + 11 * 1\\ S = 12(1 + 2 + ...+ 10) + 11\\ S = 12* \frac{10*11}{2} +11\\ S=671[/tex]

Answer 2

Sau S=1+13+25+....121; S=121+109+.....1 => 2S=122+122+....122 vom avea (121-1)/12+1=10+1=11 termeni => S=122*11/2=61*11=671