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Thread: [SOLVED] Stuck on the next step

  1. February 3rd 2010, 10:42 AM #1
    vinson24
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    [SOLVED] Stuck on the next step

    Solve e^{-2x}-3e^{-x}=-2 for x without using a calculator

    Now the first step i did was make it into a quadratic equation
    e^{-2x}-3e^{-x}+2=0
    Then i let u=e^{-x}
    which gives me u^{x}-3u+2=0
    now im kinda stuck on the next step becuase of the u^{x} in the equation, not sure if i started of wrong or if im missing something thats right in front of me
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  2. February 3rd 2010, 10:50 AM #2
    Plato
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    Multiply by e^{2x} to get 2e^{2x}-3e^{x}+1=0.
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  3. February 3rd 2010, 11:01 AM #3
    vinson24
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    at which point in the problem are you multiplying e^{2x} because i dont see where the 2e^{2x}is coming from and the 1 at the end either
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  4. February 3rd 2010, 11:03 AM #4
    wonderboy1953
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    Correction

    It's not u^x, it's u^2 in your last equation.
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  5. February 3rd 2010, 12:04 PM #5
    Plato
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    Quote Originally Posted by Plato View Post
    Multiply by e^{2x} to get 2e^{2x}-3e^{x}+1=0.
    You must know basic algebra in order to do calculus.
    e^{-2x}(e^{2x})-3e^{-x}(e^{2x})=-2(e^{2x}).
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