Question

determine a soma dos trinta primeiros termos da p.a (-8,-6,-4,-2,....)

Answer 1

P.A.(-8,-6,-,4,-2,....)
A 1 = -8
A 2 = -6
R = A 2 - A 1
R = -6 - (-8)
R = -6 + 8
R = 2

S N = N.(A 1 + A N) / 2
A 30 = A 1 + (N - 1 ).R
A 30 = -8 + (30 - 1 ).2
A 30 = -8 + (29) . 2
A 30 = - 8 + 58
A 30 = 50

S 30 = 30.(-8 + 50) / 2
S 30 = 30 . 42 / 2
S 30 = 1260 / 2
S 30 = 630