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Math Help - Where am i going wrong here?

  1. #1
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    Oct 2008
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    Where am i going wrong here?

    Where am i going wrong? I'm trying to find x using the cosine rule from:



    so i've got:

    7^2 = (x+2)^2 + 4^2 - 2\times{(x+2)}\times{4}\times(\frac{\sqrt2}{2})

    49 = x^2 + 4x + 4 + 16 - 8(x+2)\times(\frac{\sqrt2}{2})

    49 = x^2 + 4x + 20 - 4(x+2)\times(\sqrt2)

    x^2 + 4x - 29 - 4(\sqrt2)x - 8(\sqrt2)

    Now i know i've already gone wrong somewhere; the answer is:

    x^2 - 4(\sqrt2-1)x - (29+8\sqrt2) = 0

    Thanks,

    F,
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  2. #2
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    Oct 2008
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    ahhh!! I've solved it, just had to factorise to bx and c.
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