Question

Am uitat cum se rezolva : 15+16+17+....+76

Va rog ajutati-ma !

Answer 1

15+16+17+...+76=(1+2+3+...76)- (1+2+3+...14)=S76-S14=(76×77):2-(14×15):2=2926-105=2821

Answer 2

$15 + 16 + 17 + ... + 76$

$r = 1 \: (ratia)$

$n = \frac{76 - 15}{1} + 1 = 76 - 15+1 = 62$

$n - nr. \: de \: termeni$

$S = \frac{62(76 + 15)}{2} = \frac{62 \times 91}{2} = 31 \times 91 = 2821$