Question

ache a soma dos 70 primeiros termos da PA (2,5,...)

Answer 1

n = 70
a 1 = 2
a 2 = 5
r = a 2 - a 1
r = 5 - 2
r = 3
a n =  a 1 + ( n - 1 ) . r
a 70 = 2 + ( 70 - 1 ) . 3
a 70 = 2 + 69 . 3
a 70 = 2 + 207
a 70 = 209
S 70  = n. ( a 1 + a 70 )  / 2
S 70 = 70 . (2 + 209 )2
S 70 = 70 . 211 / 2
S 70 = 14770/2
S 70= 7 385