Question

Calculați suma lui gauss 5+10+15+...+275

Answer 1

$5 + 10 + 15 + ... + 275$

$= 5(1 + 2 + 3 + ... + 55)$

$= 5 \times \frac{55 (55 + 1)}{2}$

$= 5 \times \frac{55 \times 56}{2}$

$= 5 \times 55 \times 28$

$= 7700$

$Formul\check{a}\::\:1+2+3+...+n=\frac{n(n+1)}{2}$

Answer 2

5+10+15+...+275 = 5×( 1 + 2 +3 + 55)

= 5 ×[(55×56):2] = 7700