Question

determine a soma dos 30 primeiros termos da PA

a) ( 10;-2...)

B) (1;12;...)

Answer 1

a)

a1 = 10
r = -12

an = a1+(n-1).r
an= 10+(30-1).(-12)
an = -338

s30 = (10+(-338)).30/2

s30 = -3.420


b)
a1 = 1
r = 11


an = 1+(30+1).11
an= 320

s30 = (1 + 320).30/2


s30 = 4.815



valeu?