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Math Help - graph

  1. #1
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    graph

    hey sorry for the sloppy graph i attached. I don't know how to really use the graph software. And um, please don't look at the numbers on the x-axis and y-axis. I don't know how to erase them. There's number on the graph given.

    The figure shows the graph of y=x^2 and y=a-x^2 for constant a. If line segment PQ=6. What does the constant "a" equal? I don't get why the answer is 18.

    The attachment might seem a little small, the graph of the with concave down (opening down?) is the equation y=a-x^2 and the graph with concave graph is y=x^2. The line segment between the two graphs (between the two points they intersect) is PQ which equals 16.
    Attached Thumbnails Attached Thumbnails graph-graph-.jpg  
    Last edited by fabxx; September 18th 2008 at 02:19 AM. Reason: thumbnail too small
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  2. #2
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    Quote Originally Posted by fabxx View Post
    The figure shows the graph of y=x^2 and y=a-x^2 for constant a. If line segment PQ=6. What does the constant "a" equal? I don't get why the answer is 18.
    Both are quadratic functions (type of parabolas) with symmetry axis being the y-axis. So, the point where the curves of both intersect is at x_1=-3 and x_2=3. Now you only need to and equal both equations to get the point of intersection. Insert x into x^2=-x^2-a \Rightarrow 2x^2=a \Rightarrow a=18
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  3. #3
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    Both are quadratic functions (type of parabolas) with symmetry axis being the y-axis. So, the point where the curves of both intersect is at and . Now you only need to and equal both equations to get the point of intersection. Insert into
    How do you tell they have symmetry axis being the y-axis? Thanks
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