Question

soma dos 35° termos da P.A (10,8,6,4,20)

Answer 1

P.A.(10,8,6,4,2, 0.....)
r = a 2 - a 1
r = 8 - 10
r = - 2
a 35 = a 1 + (n - 1 ).r
a 35  = 10 + (35 - 1 ). -2
a 35 = 10 + (34). - 2
a 35 = 10  - 68
a 35 = - 58
S n = n . (a 1 + a n ) / 2
S 35 = 35 . (10 + (-58) / 2
S 35 = 35 . (10 - 58 ) / 2
a 35 = 35 . (- 48 ) / 2
a 35 = - 1680/2
a 35 =  - 840