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Math Help - Parabola, I think im going wrong somwhere!

  1. #1
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    Parabola, I think im going wrong somwhere!

    ok guys, I gotta graph p= -X^2 + 85X - 550

    ive got this far,

    P= f(x)

    f(x)= -X^2 + 85X - 550

    = Y = -X^2 +85X - 550

    a= -1 b=85 c=-550

    vertex(x) = -b/2a = -(85)/2(-1) = -85/-2 = 42.5



    then i started to plug it into the Y vertex and something dosen't seem right
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  2. #2
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    the 42.5 gives you the x value that you want to put into your equation you should get 1256.25, if you have a graphing calc like the TI 84 it has tools on it where you do not have to do any math and it will locate the point on the graph
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  3. #3
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    thanks for the reply,

    the way i carried it on was

    y of vertex = (-42.5)^2 + 85(42.5) - 550

    = 1806.25 + 3612.5 - 550

    = 4868.75

    where have i gone wron??
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  4. #4
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    Sorry that I didnt get back to you sooner, your mistake is (-42.5)^2

    What you need to do is -(42.5)^2+85(42.5)-550

    what we have is a -1 being multipled by 42.5^2 so we need to keep that negative seperate,

    if the equation said -2x^2+85x-550=y; you would keep that neg out right? we have to do the same thing with the negative 1, try and put then one there so you can see that after you square x then you need to multiple that be -1
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