Question

S=2+4+6+...... ....+108

Answer 1

$S = 2 + 4 + 6 + ... + 108$

$S = 2(1 + 2 + 3 + ... + 54)$

$S = 2 \times \frac{54(54 + 1)}{2}$

$S = 54(54 + 1)$

$S = 54 \times 55$

$S = 2970$

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

Answer 2

Folosim formula lui Gauss

1 + 2 + ... + n = n (n + 1) : 2

S = 2 + 4 + .. + 108

S = 2(1 + 2 + .. + 54)

S = 2(54*55 : 2)

S = 54*55

S = 2970