Question

Calculand S=4+5+6+7+ ....+100 obtinem

Answer 1

$S=(1+2+3)+4+5+...+100-(1+2+3)= \\ \\ ~~~=1+2+3+4+5+...+100-6= \\ \\ ~~~= \frac{100 \cdot 101}{2} -6= \\ \\ ~~~= 50 \cdot 101-6= \\ \\ ~~~=5050-6= \\ \\ ~~~=5044.$

Answer 2

putem face un arfificiu pentru a aplica Gauss

1+2+3+4+5+6+7+..+100 - (1+2+3)

si o sa avem 
100*101/2-6=
50*101-6=
5050-6=5044