Question

Select the best answer for the question.

2. Find the sum of the first 8 terms of a geometric series in which a1 = 3 and r= 2.​

Answer 1

Answer: Answer: 765

Work Shown:

a = 3 is the first term

r = 2 is the common ratio

Sn = a*(1-r^n)/(1-r) ... sum of the first n terms

S8 = 3*(1-2^8)/(1-2) ... sum of the first 8 terms

S8 = 3*(-255)/(-1)

S8 = 765

Answer 2

Answer: 765

=============================================

Work Shown:

a = 3 is the first term

r = 2 is the common ratio

Sn = a*(1-r^n)/(1-r) ... sum of the first n terms

S8 = 3*(1-2^8)/(1-2) ... sum of the first 8 terms

S8 = 3*(-255)/(-1)

S8 = 765

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We can generate the first 8 terms to get 3, 6, 12, 24, 48, 96, 192, 384. Each new term is found by multiplying the previous one by 2.

Then add them up to get 3+6+12+24+48+96+192+384 = 765. We get the same result.