# Geometric progression

Submitted by Don Pilas on September 20, 2019 - 5:25pm

Find the sum of the first 5 terms of the geometric progression if the third term is 144 and the sixth term is 456.?

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Submitted by Don Pilas on September 20, 2019 - 5:25pm

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- 255 reads

## The formula for the sum of

The formula for the sum of the first

nterms of geometric progression is$S_n = \dfrac{a_1(1 - r^n)}{1 - r}$

All we need to do is to find the first term

a_{1}and the common ratior.To find the common ratio use the formula

$a_n = a_m r^{n - m}$

$a_6 = a_3 r^{6 - 3}$

With

rknown, you can solve fora_{1}using the formula:$a_n = a_1 r^{n - 1}$

$a_6 = a_1 r^{6 - 1}$

With your

a_{1}andrknown, you can now calculate the sumS_{5}.## Add new comment