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Math Help - need help

  1. #1
    Junior Member
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    Jan 2007
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    need help

    i have 31.6 = 12.74(Z - 18.63)^1.15

    and i need to find Z

    i get 20.01

    can any1 confirm this?
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  2. #2
    MHF Contributor
    Joined
    Apr 2005
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    Quote Originally Posted by question View Post
    i have 31.6 = 12.74(Z - 18.63)^1.15

    and i need to find Z

    i get 20.01

    can any1 confirm this?
    Let us see.

    31.6 = (12.74)(z -18.63)^(1.15)
    31.6 / 12.74 = (z -18.63)^(1.15)
    2.480377 = (z -18.63)^(1.15)
    Raise both sides to their 1/(1.15) power,
    2.203225 = z -18.63
    2.20 +18.63 = z
    z = 20.83 ---------------answer.

    Uh-oh, that's not 20.01. It is close, though.
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by question View Post
    i have 31.6 = 12.74(Z - 18.63)^1.15

    and i need to find Z

    i get 20.01

    can any1 confirm this?
    31.6=12.74(z-18.63)^{1.15}

    divide through by 12.74:

    31.6/12.74\approx 2.4804 \approx (z-18.63)^{1.15}

    Now take logs:

    \ln(2.4804) \approx 1.15 \ln(z-18.63)

    rearrange and simplify:

    \ln(z-18.63) \approx \ln(2.4804)/1.15 \approx 0.78993

    so:

    z-18.63 \approx e^{ 0.78993}

    so:

    z \approx 18.63+e^{ 0.78993}\approx 20.833

    RonL
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