Graphing in Vertex Form and Intercept Form
What kind of functions are the following…?
y = a(x – h) 2 + k It is the graph of the parabola y = ax 2 translated horizontally h units and vertically k units. The vertex is (h, k) The axis of symmetry is x = h. Vertex Form
1. Identify the vertex and plot it. Ex: y = 3(x – 5) 2 – 8 Vertex: (5, -8) Ex: y = -½ (x + 2) Vertex: (-2, 4) Ex: y = (x + 7) 2 – 1 Vertex: (-7, -1) 2. Draw the line of symmetry through the vertex. 3. Evaluate the function for values of x near the line of symmetry and plot those points. Graphing in vertex form
Graph: y = ½(x – 3) Example
Use the calculator to graph. Notice anything? y = 2(x – 3)(x + 6) y = x(x + 4) y = (x – 5)(x – 1) If you know the x intercepts, you can plot them to help make your graph. The vertex will have an x-value that is halfway between the x-intercepts. Intercept form
y = a(x – p)(x – q) The x-intercepts are p and q. The axis of symmetry is halfway between (p, 0) and (q, 0). The graph opens up if a is positive. Example: graph y = -x(x – 4) Intercept form