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## Homework Statement

The sum of an infinite geometric sequence is 13

^{1}/

_{2}, and the sum of the first three terms is 13. Find the first term.

## Homework Equations

S

_{∞}= a/(1-r)

Sn = a-ar

^{n}/(1-r)

## The Attempt at a Solution

a/(1-r) = 13

^{1}/

_{2}

a-ar

^{3}/(1-r) = 13

2a = 27-27r ........................ 1

a-ar

^{3}= 13-13r..... 2

I'm stuck.