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Math Help - Find x

  1. #1
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    Smile Find x

    X^(4/3) - 6X^(2/3) = -8

    and

    9^(2x) - 2*9^x = 3

    Thanks!!
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  2. #2
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    These are simple quadratic forms. You must see the relationship to all other quadratics you have encountered.

    a\cdot Something^{2}\;+\;b\cdot Something\;+\;c\;=\;0

    Then, Something\;=\;\frac{-b \pm \sqrt{b^{2}-4ac}}{2a}

    This should be familiar.
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  3. #3
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    Thanks!
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  4. #4
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    Write it in that form. Show us your efforts and additional suggestions can be offered.

    Hint: 9^{2x}\;=\;\left(9^{x}\right)^{2}
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  5. #5
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    For the first equation, I got down to x^4 - 6x^2 + 2 = 0 , am I doing it right so far?
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  6. #6
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    That would depend on your substitution. What did you do? Normally, you would want to change variables. Using 'x' both before and after is certainly bad form, but mostly it's just confusing.

    Try y = x^{2/3} and write the whole thing in terms of 'y'.
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  7. #7
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    Ohhhh haha I got them now !! Should have thought of substitution
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