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Math Help - Multiplying Radicals

  1. #1
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    Multiplying Radicals

    \sqrt{-12}\times\sqrt{-27}

    My book gives -18 as the answer. Is it correct?
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  2. #2
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    √-12 √-27 = √12i √27i = 2√3i 3√3i = 6√3i = 6 3 -1 = 18 -1 = -18, hence correct.
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  3. #3
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    I see... I was making a simple mistake, again and again. Thanks for your help.
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  4. #4
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    Yes

    Given \sqrt{-1} = i then you have

    \sqrt{-1}\times \sqrt{-27} = \sqrt{12}i\times{\sqrt{27}i = \sqrt{12}\times\sqrt{27}\times i^2 = \sqrt{12}\times\sqrt{27}\time(-1) = -\sqrt{12}\times\sqrt{27}

    Beaten too it
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  5. #5
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    Thanks anyway.
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