Finding the Y-Intercept

One of the most important tools for determining the placement of a line lies with its x- and y-intercepts.

The definitions of x- and y-intercepts are as follows:

  • The x-intercept is where the graph crosses the x-axis.
  • The y-intercept is where the graph crosses the y-axis.

The difficulty for students comes in when we try to deal with intercepts algebraically. On the Cartesian plane, the y-axis is really the line "x = 0" and the x-axis is really the line y = 0. Algebraically, then:

  • An x-intercept is a point on the graph where y is zero.
  • A y-intercept is a point on the graph where x is zero.

Finding the y-Intercept

Over the week of instruction on graphing linear equations, Ms. Garcia-Anderson's students explored many different topics, including:

  1. Finding ordered pairs for an equation, y = mx + b, making a table, and graphing;
  2. Graphing linear equations using intercepts, how to find y-intercepts, and how to find x-intercepts; and
  3. Graphing linear equations that are horizontal and vertical lines.

    In the clip below, you will see her class as they focus on finding the y-intercept. Notice that she introduces the California High School Exit Examination question: Find the y-intercept of 2x - 3y =12.

The whiteboards that Ms. Garcia-Anderson uses have graph lines on them which allows her to see how her students solve the problem, and where they have trouble.

In the next clip, she asks students for the methods that they would use to solve the problem.
 


Classroom Clip Reflection:

  • How did Ms. Garcia-Anderson's questions help her students?
  • What are the implications for your work with your students?