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Math Help - Subtracting two complex Numbers

  1. #1
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    Subtracting two complex Numbers

    This is so confusing
    (8 + sqrt of -18) - (4 + 3 sqrt of 2i)
    Last edited by mr fantastic; September 14th 2009 at 05:51 AM. Reason: Changed post title and removed extraneous o's from so.
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by tsmith View Post
    This is soooooo confusing
    (8 + sqrt of -18) - (4 + 3 sqrt of 2i)
    Is it (8+\sqrt{-18})-(4+3\sqrt{2}i)?

    If so, note that \sqrt{-18}=\sqrt{9(-2)}=3\sqrt{-2}=3\sqrt{2}i

    Now simplify 8+3\sqrt{2}i-4-3\sqrt{2}i by combining the real and imaginary parts.

    Can you continue from here?
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  3. #3
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    So the 3 sqrt 2i will cancel each other out, right? So the answer would be 4?
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  4. #4
    No one in Particular VonNemo19's Avatar
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    Quote Originally Posted by tsmith View Post
    So the 3 sqrt 2i will cancel each other out, right? So the answer would be 4?
    yes.
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  5. #5
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    That is, assuming you meant 4+ 3i\sqrt{2} and not 4+ 3\sqrt{2i}. Not being able to tell is that "i" is inside or outside the square root is a good reason to always write "i" in front of square roots, not behind them.
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