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3.2 Graphing Quadratic Functions in Vertex or Intercept Form
Definitions 3 Forms Graphing in vertex form Examples Changing between eqn. forms

Quadratic Function A function of the form y=ax2+bx+c where a≠0 making a u-shaped graph called a parabola. Example quadratic equation:

Vertex- Axis of symmetry- The lowest or highest point of a parabola.
The vertical line through the vertex of the parabola. Axis of Symmetry

Vertex Form Equation y=a(x-h)2+k If a is positive, parabola opens up
If a is negative, parabola opens down. The vertex is the point (h,k). The axis of symmetry is the vertical line x=h.

Vertex Form (x – h)2 + k – vertex form
Each function we just looked at can be written in the form (x – h)2 + k, where (h , k) is the vertex of the parabola, and x = h is its axis of symmetry. (x – h)2 + k – vertex form Equation Vertex Axis of Symmetry y = x2 or y = (x – 0)2 + 0 (0 , 0) x = 0 y = x2 + 2 or y = (x – 0)2 + 2 (0 , 2) y = (x – 3)2 or y = (x – 3)2 + 0 (3 , 0) x = 3

Analyze y = (x + 2)2 + 1. Example 1: Graph
Step 1 Plot the vertex (-2 , 1) Step 2 Draw the axis of symmetry, x = -2. Step 3 Find and plot two points on one side , such as (-1, 2) and (0 , 5). Step 4 Use symmetry to complete the graph, or find two points on the left side of the vertex.

Your Turn! Analyze and Graph: y = (x + 4)2 - 3. (-4,-3)

Example 2: Graph y=-.5(x+3)2+4
a is negative (a = -.5), so parabola opens down. Vertex is (h,k) or (-3,4) Axis of symmetry is the vertical line x = -3 Table of values x y -1 2 -3 4 -5 2 Vertex (-3,4) (-4,3.5) (-2,3.5) (-5,2) (-1,2) x=-3

Table of values with 5 points?
Now you try one! y=2(x-1)2+3 Open up or down? Vertex? Axis of symmetry? Table of values with 5 points?

(-1, 11) (3,11) X = 1 (0,5) (2,5) (1,3)

Changing from vertex or intercepts form to standard form
The key is to follow ORDER OF OPERATIONS Ex: y=-(x+4)(x-9) Ex: y=3(x-1)2+8 =-(x2-9x+4x-36) =3(x-1)(x-1)+8 =-(x2-5x-36) =3(x2-x-x+1)+8 y=-x2+5x =3(x2-2x+1)+8 =3x2-6x+3+8 y=3x2-6x+11

Changing from vertex or intercepts form to standard form
Practice: 1: y = 3(x-4)(x+2) 2: y = -2(x-3)2 - 5

Challenge Problem Write the equation of the graph in vertex form.

Practice Workbook Page 68 #16-21

Assignment Book Page 66 #25-33 and Page 68 #27, 28

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