Question

What is the sum of the geometric sequence 8, 15, 22..., if there are 26 terms?

Answer 1

a₂-a₁=15-8=7

a₃-a₂=22-15=7

d=7

aₙ=a₁+d(n-1)

a₂₆=8+7*(26-1)=8+7*25=183

S₂₆=(a₁+a₂₆)*26/2=(8+183)*26/2=2483