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Math Help - Not sure I'm doing this the right way

  1. #1
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    Not sure I'm doing this the right way

    I need to solve this in terms of x

    3y(3y-x) = 2z(x+2z)

    9y2 - 3yx = 2zx + 4z2

    9y2 - 4z2 = 3yx + 2zx

    (9y - 4z)(9y + 4z) = x(2z + 3y)

    x = (9y - 4z)(9y + 4z) / (2z + 3y)

    don't know if I can cancel to give this

    x = (3y - 2z)(3y + 2z)

    x = 9y2 + 3y2z - 3y2z - 4b2

    x = 9y2 - 4b2


    Really don't know if I've done this properly. Can anyone help?

    Thanks.
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  2. #2
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    Re: Not sure I'm doing this the right way

    Quote Originally Posted by kx110 View Post
    I need to solve this in terms of x

    3y(3y-x) = 2z(x+2z)

    9y2 - 3yx = 2zx + 4z2

    9y2 - 4z2 = 3yx + 2zx

    (9y - 4z)(9y + 4z) = x(2z + 3y)

    x = (9y - 4z)(9y + 4z) / (2z + 3y)
    this is as far as you can go ...
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  3. #3
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    Re: Not sure I'm doing this the right way

    I thought it might be, I was just guessing with the rest. Do you think it's necessary to convert 9y2 - 4z2 to (9y - 4z)(9y + 4z) or is that over complicating it?

    Thanks for your help.
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  4. #4
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    Re: Not sure I'm doing this the right way

    Quote Originally Posted by kx110 View Post
    I thought it might be, I was just guessing with the rest. Do you think it's necessary to convert 9y2 - 4z2 to (9y - 4z)(9y + 4z) or is that over complicating it?

    Thanks for your help.
    it's a matter of choice ... I prefer to have it factored in case one has to find zeros of the expression, etc.
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