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Homework Help: Finding the equations of a graph

  1. Mar 9, 2009 #1
    I am trying to do a College Algebra project and I am having difficulty findimg the two equations that make the piecewise function in the pictures below.

    Letting y be the number of meters the track is above or below the ground
    and x the number of meters horizontally from the high point, write the
    equation/s expressing y in terms of x for the roller coaster track. The
    parabola changes from turning down to turning up at x = 15.

    Last edited: Mar 9, 2009
  2. jcsd
  3. Mar 9, 2009 #2


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    Science Advisor

    Are you given that it is a "parabola"? If so your graph can't possibly be right. A parabola is always concave upward or always concave downward.

    If, instead, this might be cubic, which is what your graph looks like, then y= [itex]ax^3+ bx^2+ cx+ d[/itex] and putting in four values for x and y gives you four linear equations to solve for a, b, c, d.

    Last edited by a moderator: Mar 10, 2009
  4. Mar 9, 2009 #3
    It is TWO different parabolas thus a piecewise function, One parabola opening downward and one opening upward. The downward opening parabola ends at (15,12.25) and the upward opening parabola starts at (15,12.25)
  5. Mar 9, 2009 #4
    I believe that the problem is that the graph is badly drawn, If I could find the vertex of the two parabolas I could easily find the leading coefficient and have my equation in a matter of seconds, but the axis arent labeled properly nor is the line very well.
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