# Maths

The sum of the first and second terms of an geometry series is 9.the sum to infinit is 12.calculate the possible values of r.

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1. a + ar = 9
a(1+r) = 9
a = 9/(1+r)

a/(1-r) = 12
a = 12(1-r)

12(1-r) = 9/(1+r)
1 - r^2 = 3/4
4 - r^2 = 3
-r^2 = -1
r = ± 1

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posted by Reiny

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