Education Technology

Lines in the Plane

Published on 06/09/2008

Activity Overview

In this activity, students create a slope triangle and understand the concepts of slope and the equation of lines. They realize that slope is constant at all points along a fixed line. They also explore the slopes of parallel and perpendicular lines.

Before the Activity

Install the Cabri™: Jr. App on the students' graphing calculators using one of these two methods:

  • TI-Connect™,  a TI Connectivity Cable, and the Unit-to-Unit Link Cable
  • TI-Navigator™  "send to class" feature
  • See the attached PDF file for detailed instructions for this activity
  • Print pages 1 - 7 from the attached PDF file for your class
  • During the Activity

    Distribute the pages to your class.

    Follow the Activity procedures:

  • Draw a horizontal segment and construct a point on the y-axis
  • With the length of the segment as radius, draw a circle with the point as the center
  • Enlarge the circle so that the point in the first quadrant is in the upper right corner of the screen
  • Construct a point on the circle in the first quadrant and draw a line connecting it to the center
  • Hide the circle and the segment, and construct 2 points, A and C, on the line
  • Draw a perpendicular from C to the X-axis, and a perpendicular from A to the Y-axis
  • Label the intersection of the perpendiculars as B
  • Hide the perpendicular lines, draw segments AB and BC, measure their lengths, and compute the ratio BC/AB
  • Drag A or C along the line and observe the variation in the value of the ratio
  • Display the equation of the line and its slope
  • Rotate the line around the y-intercept and examine the relationship between the slope and the equation
  • Observe the changes in the equation as the y-intercept is changed
  • Explore the slopes of parallel and perpendicular lines and determine the products of the slopes of perpendicular lines
  • After the Activity

    Review student results:

  • As a class, discuss questions that appeared to be more challenging
  • Re-teach concepts as necessary