Quadratics - Intercept form

Students found out yesterday that graphing quadratics in standard form does not lend itself well for locating the x-intercepts. Sometimes the graph crosses between two "nice" integers. Sometimes the graph crosses the x-axis a significant distance away from the vertex and requires extra work to locate. So, today's lesson is about the intercept form which identifies the x-intercepts very easily.

Intercept form: y = a (x - p) (x - q)

• To find the x-intercepts in this form, set the factors equal to 0 and solve for x: (p, 0) and (q, 0).
• To find the vertex and the axis of symmetry in this form, remember that the graph is symmetrical, meaning that the AOS will have to be in the middle of the intercepts. To find this location, average p and q. This calculates the x-value of the vertex. Substitute this into the equation and solve for y.
• Pick another value for x near the vertex and find it corresponding y value. Plot all points and draw a smooth U-shaped curve.

Homework: Worksheet on Graphing Quadratics in Intercept Form

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