Question

calcule a soma dos 25 primeiros termos da PA (1,3,5...)

Answer 1

P.A.(1,3,5,...)
A 1 = 1
r = a 2 - a 1
r = 3 - 1
r =2
a 25 = a 1 + (n - 1 ).r
a 25 = a 1 + (25 - ).2
a 25 = 1 + 24 . 2
a 25 = 1 + 48
a 25 = 49
S  n = n . ( a 1 + a n) / 2
S25 = 25 . (1 + 49) /2
S 25 = 25 . 50 /2
S 25 = 1250/2
S 25 = 625