# Geometric Series (Algebra 2)

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I need some assistance or a formula when trying to find the first term of geometric series please! I don't understand this!!!!

What is the first term of a geometric series with a summation of 289, 5 terms and a common ratio of 1/2?

• Geometric Series (Algebra 2) -

g + g r + g r^2 + g r^3 + g r^4 = 289

g (1 + 1/2 + 1/4 + 1/8 + 1/16) = 289

find sum of
1 + 1/2 + 1/4 + 1/ 8 + 1/16
S5 = [1-(1/2)^5]/(1/2) = 31/16
so
g (31/16) = 289
g = 149.16

• Geometric Series (Algebra 2) -

Thank you Damon, that helped alot...

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