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Math Help - I need help with parabolas and graphing them, PLease help!

  1. #1
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    I need help with parabolas and graphing them, PLease help!

    There's a few, but anything would help me!

    3. sketch the graph of the quadratic function using the vertex, y-intercept, and symmetric point.

    a.vertex: (-1,4) and y-intercept: 7

    b. Vertex: (-3, -4) and y-intercept : 0

    4. Find tgr orderd pair of the vertex using either algebraic method (vertex form or the folmula drived from the Quadratic formula)
    a. y=x^2-8x+15

    b. y=-3x^2-1x-15
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  2. #2
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    Quote Originally Posted by Kayla View Post
    There's a few, but anything would help me!

    3. sketch the graph of the quadratic function using the vertex, y-intercept, and symmetric point.

    a.vertex: (-1,4) and y-intercept: 7
    Plot the point (-1,4) in your x-y plane. Then plot 7 on the y-intercept.

    Now join the point to the y-intercept.


    Quote Originally Posted by Kayla View Post
    4. Find tgr orderd pair of the vertex using either algebraic method (vertex form or the folmula drived from the Quadratic formula)
    a. y=x^2-8x+15
    You need to complete the square here, i'll do the first one, you can try the second.

    y=x^2-8x+15

    Take the coefficent of x , half it then square it to give a new constant term.

    y=\left(x^2-8x+\left(\frac{-8}{2}\right)^2\right)<br />
+15-16

    y=\left(x^2-8x+16\right)-1

    y=(x-4)^2-1

    giving a vertex of (4,-1)
    Last edited by pickslides; March 1st 2010 at 12:46 PM.
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  3. #3
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    I need the most help with y=-3x^2-12x-7 because of the -3x^2, My teacher tried to tell me to divide by -3, I still do not understand.
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  4. #4
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     y=-3x^2-12x-7 = -3\left(x^2+4x+\frac{7}{3} \right)<br />


    Now complete the square as shown previously inside the brackets.
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