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# The sum of the first 3 terms of a geometric series is 171 and the common ratio is 2/3.

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The sum of the first 3 terms of a geometric series is 171 and the common ratio is 2/3.

What is the first term of the series?

I Don't know what to do- it says I have to use formula?

Aug 6, 2019

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first off do you know what a geometric series is?

Aug 6, 2019
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Yep!

tommarvoloriddle  Aug 6, 2019
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$$\text{well then you should know that the sum of the first three terms are}\\ a + \dfrac 2 3 a + \dfrac 4 9 a = \dfrac{19}{9}a = 171\\ a=81$$

Rom  Aug 6, 2019
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ok, thank you, Rom!

I got that answer too, I just forgot to post it...

tommarvoloriddle  Aug 6, 2019