math(log)

find x if

a) 1/81=3^2x-1

b)log2x+ 3/log2x = 4

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asked by fizz
  1. since 81 = 3^4, we have

    3^-4 = 3^(2x-1)
    -4 = 2x-1
    x = -3/2

    logx + 3/logx = 4
    log^2(x) - 4logx + 3 = 0
    (logx-1)(logx-3) = 0
    logx = 1,3
    x = 2,8
    check:
    1+3/1 = 4 yes
    3+3/3 = 4 yes

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    posted by Steve
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    posted by fizz

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