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Thread: Surds - addition and and subtraction

  1. November 20th 2009, 08:59 PM #1
    BeVs
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    Surds - addition and and subtraction

    Simplify:

    6\sqrt{44}+4\sqrt{120}-\sqrt{99}-3\sqrt{120}

    12\sqrt{11}+8\sqrt{30}-3\sqrt{11}-3\sqrt{30}

    9\sqrt{11}+5\sqrt{30} \ \ \ \ \ \ \ \text{:my answer}

    9\sqrt{11}+\sqrt{30} \ \ \ \ \ \ \ \ \text{:text book answer}

    Where have I gone wrong!


    .
    Last edited by CaptainBlack; November 21st 2009 at 07:46 AM.
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  2. November 20th 2009, 09:31 PM #2
    Unenlightened
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    Quote Originally Posted by BeVs View Post
    Simplify:

    6\sqrt{44}+4\sqrt{120}-\sqrt{99}-3\sqrt{120}

    12\sqrt{11}+8\sqrt{30}-3\sqrt{11}-3\sqrt{30}

    9\sqrt{11}+5\sqrt{30} \ \ \ \ \ \ \ \text{:my answer}

    9\sqrt{11}+\sqrt{30} \ \ \ \ \ \ \ \ \text{:text book answer}

    Where have I gone wrong!

    Obviously the discrepancy is with your -3\sqrt{270} part.
    This equals -3\sqrt{9}\sqrt{30} = -3*3\sqrt{30} = -9 \sqrt{30}
    So then your +8\sqrt{30}-9\sqrt{30} = -\sqrt{30}
    So you should have 9 \sqrt {11}- \sqrt {30}...

    Which is different from the text book answer you gave... are you sure you took it down correctly?
    Last edited by CaptainBlack; November 21st 2009 at 07:46 AM.
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  3. November 20th 2009, 11:04 PM #3
    BeVs
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    ah many thanks, yeh sry, its a - sign at the end ^.^
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