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Math Help - Solve by factoring/completing the square

  1. #1
    Mad
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    Solve by factoring/completing the square

    If you can't solve by factoring, solve by completing the square.

    27. y^2 - 2y = 17



    I can't remember how to solve by completing the square. If someone could help with this one, I should be able to remember.
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  2. #2
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    y^2 -2y = 17

    (y - 1)^2 -1 = 17

    (y -1)^2 = 18

    y - 1 = +/- sqrt 18

    y = 1 +/- 3 sqrt 2
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  3. #3
    Mad
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    Okay, so I still don't understand how you knew to do that exactly. And I'm pretty sure we didn't do this in class...I don't remember this at all.

    6y^2 - 5y = 4
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  4. #4
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    This one can be solved by factoring.

    6y^2 - 5y - 4 = 0

    (3y - 4)(2y + 1) = 0

    Expanding this using FOIL might help you to understand how I factored.

    Set each factor to 0 and solve for y.

    3y - 4 = 0

    3y = 4

    y = 4/3

    and

    2y + 1 = 0

    2y = -1

    y = - 1/2

    Do you understand that?
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  5. #5
    Mad
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    Yeah, I do, I didn't realize it could be factored. Thanks.
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