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Math Help - Distance Formula

  1. #1
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    Distance Formula

    I'm really having a hard time with this. It deals with distance formula.

    http://i35.tinypic.com/2j5hztf.jpg

    As you can see from that picture, I tried solving the problem and got 117 as an answer. But my teacher told me the answer was 3√13 but I have no idea how.

    Please elaborately explain to me how I could arrive to the correct answer. Thank You
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  2. #2
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    \sqrt{117}= \sqrt{9\times 13} = \sqrt{9}\sqrt{ 13}= 3\sqrt{ 13}
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  3. #3
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    Quote Originally Posted by GLAMX View Post
    I'm really having a hard time with this. It deals with distance formula.

    http://i35.tinypic.com/2j5hztf.jpg

    As you can see from that picture, I tried solving the problem and got 117 as an answer. But my teacher told me the answer was 3√13 but I have no idea how.

    Please elaborately explain to me how I could arrive to the correct answer. Thank You
    Actually sqrt(117) = 3*sqrt(13). However, although it is correct, it is not in the form the teacher expects. You need to factor out squares when possible. It's actually not that bad. You probably will only need to check 1, 4, 9, 16, 25, 36, 49 anyway.

    Now, 117 = 9 * 13, so
    sqrt(117) = sqrt(9*13)

    but. we know sqrt(a*b) = sqrt(a)sqrt(b) [exponent rule], so

    sqrt(9*13) = sqrt(9)*sqrt(13) = 3 * sqrt(13), and we are done.
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  4. #4
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    Quote Originally Posted by pickslides View Post
    \sqrt{117}= \sqrt{9\times 13} = \sqrt{9}\sqrt{ 13}= 3\sqrt{ 13}

    Thank you. This was very helpful. Just one more question, the 9 and 13, does it have to be those specific numbers? Or can they be two numbers that equal to 117?
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  5. #5
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    You have to find a factor of 117 that is a square number.

    I.e. 1^2 = 1, 2^2 = 4, 3^2= 9 , 4^2=16, \dots

    Factoring into 2 numbers that aren't square will not have the desired affect.
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