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The 65th therm in a geometric sequence is 8000, and the 69th term is 500, find the 64th term using the geometric series sum formula

  • math -

    ar^64 = 8000
    ar^68 = 500
    divide the second by the first...
    r^4 = 1/16
    r = ± 1/2

    so if term(65) = 8000, and r = ± 1/2
    then term(64) = 8000/r = 8000/±1/2 = ± 16000

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