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Thread: Probably right for the wrong reason: complete square for -x^2 - 12x

  1. #1

    Probably right for the wrong reason: complete square for -x^2 - 12x

    1. LarCalcET6 5.8.037.

    Find or evaluate the integral by completing the square:


    . . . . .[tex]\displaystyle \int\, \dfrac{1}{\sqrt{\strut -x^2\, -\, 12x\,}}\, dx[/tex]



    So when I did complete the square I did

    -x^2 -12x
    = -(x^2 + 12x)
    = -(x^2 +12x +36) - 36
    = -36 - (x + 6)^2

    I didn't know what to do with the negative so I just ignored it and got the right answer but I feel like I cheated. That negative in front of the x is what F'd me up.

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    Last edited by stapel; 02-02-2018 at 03:11 PM. Reason: Typing out the text in the graphic; creating useful subject line.

  2. #2
    Junior Member
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    Looks like you have -36 twice instead of +36 and -36.

  3. #3
    Quote Originally Posted by lev888 View Post
    Looks like you have -36 twice instead of +36 and -36.
    Thank you

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