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Math Help - X Solve Check

  1. #1
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    X Solve Check

    I am solving for X below:

    43x+5 = 1/256


    The answer I get is -3 please correct me if I am wrong and why if you can please. Much appreciated.
    Last edited by gbrad88; December 2nd 2012 at 07:18 PM.
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  2. #2
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    Re: X Solve Check

    Some brackets where they're needed would be nice.
    Thanks from itgl72 and topsquark
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  3. #3
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    Re: X Solve Check

    I would like to learn how to do that too.
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  4. #4
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    Re: X Solve Check

    Well as it's written we can't tell if you meant \displaystyle \begin{align*} 4^{3x + 5} = \frac{1}{256} \end{align*} or \displaystyle \begin{align*} 4^{3x} + 5 = \frac{1}{256}  \end{align*} or even \displaystyle \begin{align*} 4^3\,x + 5= \frac{1}{256} \end{align*}. Simply by putting what you meant to have as the power in brackets can overcome this ambiguity.
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  5. #5
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    Re: X Solve Check

    Im looking for the first example:


    43x+5 = 1/256


    Thank you, sorry for formatting.
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  6. #6
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    Re: X Solve Check

    From here, it's just a matter of expressing the RHS as a power of 4:

    \frac{1}{256}=4^{-4}

    Now, equate exponents, and solve for x.
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  7. #7
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    Re: X Solve Check

    Quote Originally Posted by MarkFL2 View Post
    From here, it's just a matter of expressing the RHS as a power of 4:

    \frac{1}{256}=4^{-4}

    Now, equate exponents, and solve for x.
    Im sorry? I dont follow you.
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  8. #8
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    Re: X Solve Check

    Surely you know that \displaystyle \begin{align*} \frac{1}{256} = \frac{1}{4^4} = 4^{-4} \end{align*}.

    So if \displaystyle \begin{align*} 4^{3x+5} = 4^{-4} \end{align*} what do you think the next step should be?
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  9. #9
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    Re: X Solve Check

    I'm having some trouble with this over all. I can go through it and get answers of either x = -1/3 or x = -3. Can someone help me with an example of doing it correctly. My mind is hitting the wall.
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  10. #10
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    Re: X Solve Check

    4^3x+5 = 1/256
    -----
    4^(3x+5) = 2^(8)
    ---
    2^(6x+10) = 2^8
    -----
    6x + 10 = 8
    6x = -2
    x = -1/3
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  11. #11
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    Re: X Solve Check

    1/256 is 2-8 = 1/(28).

    therefore, you should have:

    6x + 10 = -8

    try again.
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  12. #12
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    Re: X Solve Check

    Quote Originally Posted by Deveno View Post
    1/256 is 2-8 = 1/(28).

    therefore, you should have:

    6x + 10 = -8

    try again.
    6x + 10 = -8

    6x=-18
    -- --
    6 6

    x=-3
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  13. #13
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    Re: X Solve Check

    now plug x = -3 back into your original equation....does it work?
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  14. #14
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    Re: X Solve Check

    I get 4^(-4) which = 1/256

    So it is TRUE, correct?

    My answer is then -3.
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