Question

calcule a soma dos termos da PA (-16,-14,-12,...84)

Answer 1

a2 - a1 = razão

- 14 - ( -16) = r

r = 2

$an = a1 + ( n - 1) .r$

84 = -16 + (n-1).2

84 +16 = 2n - 2

100 + 2 = 2n

n = 51

$S = \frac{(a1 + an) . n }{2}$

$S = \frac{(-16 + 84 ) . 51 }{2}$

Soma = 1734

Answer 2

Sn=(a1+an).n/2
Sn=(-16+84).51/2
Sn=68.51/2
Sn=3468/2
Sn=1734