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Math Help - Finding values of quadratic equation

  1. #1
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    Finding values of quadratic equation

    Got a math sum I'm working on thats troubling me.

    {x}^{2} + 4x - 8 can be written in the form {(x + p)}^{2} + q

    Find the values of p and q
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  2. #2
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    Quote Originally Posted by yorkey View Post
    Got a math sum I'm working on thats troubling me.

    {x}^{2} + 4x - 8 can be written in the form {(x + p)}^{2} + q

    Find the values of p and q
    You have two options, both require that you have the necessary knowledge and understanding.

    Option 1: Complete the square for x^2 + 4x - 8 and compare with (x + p)^2 + q.

    Option 2: Expand (x + p)^2 + q and equate the coefficients of the various powers of x with the corresponding coefficients in x^2 + 4x - 8.
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  3. #3
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    Ok great! Thanks

    p = 2
    q = -8

    Does that work?
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  4. #4
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    {(x + 2)}^{2} - 8= x^2+2x+2x+4-8= x^2+4x-4 .

    So p looks correct, but q does not. You almost got it though.
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  5. #5
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    Oh I'm a retard. My reasoning went something like this:

    (x + 2)^2 is expanded to x^2 + 4, which it obviously is NOT. So q is -12, right?
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  6. #6
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    Quote Originally Posted by yorkey View Post
    Oh I'm a retard. My reasoning went something like this:

    (x + 2)^2 is expanded to x^2 + 4, which it obviously is NOT. So q is -12, right?
    Hi yorkey,

    Yes, q = -12

    Complete the square on x^2+4x+4

    (x^2+4x\: {\color{red}+4})-8 \: {\color{red}-4}

    (x \: {\color{red}+2})^2\: {\color{red}-12}
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  7. #7
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    Y'all are legends, thanks.

    /this case is closed
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