Question

calcule a soma dos 80 primeiros termos da p a (-60,-51,-42)

Answer 1

r = -51 - 60
r = -111
an = a1+(N-1).R
an = -60+(80-1).(-111)
an = -60+79.(-111)
an = -60 - 8679
an = -8829

Sn = (a1+an\).n/2
Sn = (-60-8829).80/2
Sn = -8889 . 40
Sn = -355560