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Math Help - rationalise the denominator

  1. #1
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    rationalise the denominator

    i am stuck rationalising the denominator of this -

    (9√6 -8)/(√6 -1)

    the book says (46 + √6) / 5

    but i keep coming out with a numerator of 28 + √6 or something. if someone could step me through it the help would be much appreciated. thanks!

    p.s my first ever time posting, i think this is the right section for this problem ^_^
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  2. #2
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    Quote Originally Posted by jacobc View Post
    i am stuck rationalising the denominator of this -

    (9√6 -8)/(√6 -1)

    the book says (46 + √6) / 5

    but i keep coming out with a numerator of 28 + √6 or something. if someone could step me through it the help would be much appreciated. thanks!

    p.s my first ever time posting, i think this is the right section for this problem ^_^

    \displaystyle \frac{9\sqrt{6}-8}{\sqrt{6}-1} \cdot \frac{\sqrt{6}+1}{\sqrt{6}+1} = \frac{54+\sqrt{6}-8}{6-1} = \frac{46+\sqrt{6}}{5}
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  3. #3
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    e^(i*pi)'s Avatar
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    You're allowed to have a surd in the numerator and as you have the right denominator I assume it's an expansion error.

    If you use FOIL on (9\sqrt{6} - 8)(\sqrt{6}+1) and collect like terms you should get the book's answer


    Spoiler:
    54+9\sqrt{6}-8\sqrt{6}-8
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  4. #4
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    thanks guys, i cant believe the mistake i made, i had 9*6 as 36 for some reason *Facepalm*
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