Question

Calcule a soma dos n termos da P.A (-20,-15,-10,5,10,15)

Answer 1

Boa tarde

PA (-20,-15,-10,5,10,15)

a1 = -20
a2 =
r = a2 - a1 = -15 + 20 = 5
an = 15 
n = 6

Sn = (a1 + an)*n/2
Sn = (-20 + 15)*6/2
Sn = -15