Question

1) Determine a soma dos termos de cada PA

a) (3,11,19,...,115)

Answer 1

r=a2-a1

r=11-3=8

an=a1+(n-1).r

3+(n-1).8=115

3+8n-8=115

8n-5=115

8n=115+5

8n=120

n=120/8

n=60/4

n=30/2

n=15

sn=n.(a1+an)/2

s15=15.(3+115)/2

s15=15.118/2

s15=15.59

s15=15.(59+1)

s15=900-15

s15=885

espero ter ajudado!

boa noite!