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Math Help - Solve the equation

  1. #1
    Senior Member Mukilab's Avatar
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    Solve the equation

    How would I go about solving this?

    6x^2+17x-39=0

    EDIT: Factorised into (-13+-3x)(3+-2x)=0But that didn't help
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  2. #2
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    Quote Originally Posted by Mukilab View Post
    How would I go about solving this?

    6x^2+17x-39=0

    EDIT: Factorised into (-13+-3x)(3+-2x)=0But that didn't help
    You have that (-13 - 3x)(3 - 2x) = 0 . Therefore either (3 - 2x) = 0 , or (-13 - 3x) = 0.

    Can you solve from here?
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  3. #3
    Senior Member Mukilab's Avatar
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    (3 - 2x) = 0 , or (-13 - 3x) = 0.

    therefore

    x=1.5 or x=\frac{-13}{3}

    It has to be one definite answer though. It tells me from this I should be able to calculate a side in a polygon (I need to find x). Do I try subbing both into the formula and see which works?
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  4. #4
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by Mukilab View Post
    (3 - 2x) = 0 , or (-13 - 3x) = 0.

    therefore

    x=1.5 or x=\frac{-13}{3}

    It has to be one definite answer though. It tells me from this I should be able to calculate a side in a polygon (I need to find x). Do I try subbing both into the formula and see which works?
    If you're measuring a side on a polygon is follows that x>0 as you're measuring a length. So discard the negative root
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  5. #5
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    Quote Originally Posted by Mukilab View Post
    (3 - 2x) = 0 , or (-13 - 3x) = 0.

    therefore

    x=1.5 or x=\frac{-13}{3}

    It has to be one definite answer though. It tells me from this I should be able to calculate a side in a polygon (I need to find x). Do I try subbing both into the formula and see which works?
    Both are correct answers to the equation, but only one is the answer you seek for the given problem. Only one of the answers makes sense as the length of a polygon's side, can you see which one and why?
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  6. #6
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    Quote Originally Posted by Mukilab View Post

    Do I try subbing both into the formula and see which works?
    Not really, you can do it as a check, both should give 0.
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  7. #7
    Senior Member Mukilab's Avatar
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    Quote Originally Posted by e^(i*pi) View Post
    If you're measuring a side on a polygon is follows that x>0 as you're measuring a length. So discard the negative root
    Ok

    Quote Originally Posted by pomp View Post
    Both are correct answers to the equation, but only one is the answer you seek for the given problem. Only one of the answers makes sense as the length of a polygon's side, can you see which one and why?
    Quote Originally Posted by pickslides View Post
    Not really, you can do it as a check, both should give 0.
    Thank you for all the posts, most considerate.
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