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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asked by Andile
  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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