Question

Dada a p.a ( -51,-47,-43...) determine

a) O 30° termo. B) a soma dos 30

primeiros termos

Answer 1

r = 4

a1 = -51

A) a30 = ?

 an = a1+(n-1)*r

 a30 = -51+(30-1)*4

 a30 = -51+29*4

 a30 = 65

B) s30 = ?

sn = [(a1+an)*n]/2

s30 = [(-51+65)*30]/2

s30 = 210