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Math Help - Solving for a variable

  1. #1
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    Solving for a variable

    I was hoping to receive some help I'm trying to solve for the variable r.

    136.89=65.33 * ((r + 4) * (r + 4) - (4 * 4)) / 12


    Thanks in advanced.
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  2. #2
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    Quote Originally Posted by Henningfeld View Post
    I was hoping to receive some help I'm trying to solve for the variable r.

    136.89=65.33 * ((r + 4) * (r + 4) - (4 * 4)) / 12


    Thanks in advanced.
    Same way you'd solve for x in

    1=2*(x^2+3x+4)/5

    Is it easier to see this way?
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  3. #3
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    I'm sorry it still has me confused. It has been a few years since I have had to touch an equation like this. I seem to what to start in the wrong directions by multiple by 12 to cancel and then divide by 65.33. In your equation I'm not sure where the 3x comes from. Any suggestions?
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  4. #4
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    Quote Originally Posted by Henningfeld View Post
    I seem to what to start in the wrong directions by multiple by 12 to cancel and then divide by 65.33.
    This is actually in the right direction.

    Quote Originally Posted by Henningfeld View Post
    In your equation I'm not sure where the 3x comes from.
    Expand (r + 4) * (r + 4) - (4 * 4) and you'll see why I put that in there.
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  5. #5
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    When I expand that I get (r^2 + 8r + 16) (-16) those two will cancel leaving (r^2 +8r) is this correct?
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  6. #6
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    Quote Originally Posted by Henningfeld View Post
    When I expand that I get (r^2 + 8r + 16) (-16) those two will cancel leaving (r^2 +8r) is this correct?
    Yes, continue.
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  7. #7
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    So in a whole equation I have this left 24.95515 = (r^2 + 8r). This is where I begin to second guess what should come next. Do I take the square root of r^2 on both sides then add r to 8r to make 9r then divide by 9?
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  8. #8
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    Quote Originally Posted by Henningfeld View Post
    So in a whole equation I have this left 24.95515 = (r^2 + 8r). This is where I begin to second guess what should come next. Do I take the square root of r^2 on both sides then add r to 8r to make 9r then divide by 9?
    I think you've made a typo somewhere, because 136.89*12/65.33 is approximately 25.1443.

    In any case, recall that for ax^2+bx+c=0 we can use the quadratic equation.
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