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Math Help - Completing the Square

  1. #1
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    Sep 2007
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    Completing the Square

    Okay. I have this problem that I have solved several times. I keep getting the same answer, but when I plug it in it is wrong. What am I doing wrong?

    2x^(2)-5x=7

    x^(2)-(5/2)x=(7/2)

    x^(2)-(5/2)x+(25/16)=(7/2)+(25/16)

    (x-(5/2))^(2)=(81/16)

    x-(5/2)=(+/-)(9/4)=(5/2)

    final answer: (19/4) or (1/4)
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  2. #2
    MHF Contributor
    Joined
    Apr 2005
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    Quote Originally Posted by ladylc15 View Post
    Okay. I have this problem that I have solved several times. I keep getting the same answer, but when I plug it in it is wrong. What am I doing wrong?

    2x^(2)-5x=7

    x^(2)-(5/2)x=(7/2)

    x^(2)-(5/2)x+(25/16)=(7/2)+(25/16)

    (x-(5/2))^(2)=(81/16)

    x-(5/2)=(+/-)(9/4)=(5/2)

    final answer: (19/4) or (1/4)
    Why is it (x -(5/2))^2 ?
    Should it not be (x -(5/4))^2 ?
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  3. #3
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    Sep 2007
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    That would be my stupid mistake, and you just fixed it. Thanks so much!
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