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Math Help - surd maths question :S

  1. #1
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    surd maths question :S

    Hey, i've been doing a maths practice paper for revision but i've come across a question i don't understand. Can anyone help me??

    Find the exact roots of the equation 2x(squared)+8x-5=0 giving your answers in their simplest form.

    The answer is -2(plus or minus)1/2 (square root) 26
    but i just keep getting -2(plus or minus) (square root) 24
    :S i don't know where i'm going wrong

    Thanks for your help
    xx
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by bubbylgirl View Post
    Hey, i've been doing a maths practice paper for revision but i've come across a question i don't understand. Can anyone help me??

    Find the exact roots of the equation 2x(squared)+8x-5=0 giving your answers in their simplest form.

    The answer is -2(plus or minus)1/2 (square root) 26
    but i just keep getting -2(plus or minus) (square root) 24
    :S i don't know where i'm going wrong

    Thanks for your help
    xx
    Hi bubblygirl,

    You probably made a simple error somewhere.

    x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}

    x=\frac{-8\pm\sqrt{8^2-4(2)(-5)}}{2(2)}

    x=\frac{-8\pm\sqrt{104}}{4}

    x=\frac{-8\pm\sqrt{4\cdot26}}{4}

    x=\frac{-8\pm2\sqrt{26}}{4}

    x=\frac{-8}{4}\pm\frac{2}{4}\sqrt{26}

    x=-2\pm\frac{1}{2}\sqrt{26}
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  3. #3
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    Quote Originally Posted by masters View Post
    Hi bubblygirl,

    You probably made a simple error somewhere.

    x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}

    x=\frac{-8\pm\sqrt{8^2-4(2)(-5)}}{2(2)}

    x=\frac{-8\pm\sqrt{104}}{4}

    x=\frac{-8\pm\sqrt{4\cdot26}}{4}

    x=\frac{-8\pm2\sqrt{26}}{4}

    x=\frac{-8}{4}\pm\frac{2}{4}\sqrt{26}

    x=-2\pm\frac{1}{2}\sqrt{26}

    ohhhhh i forgot that its minus 5 and a minus X a minus is a plus
    thanks sooo much
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