# Activities

• • • ##### Subject Area

• Math: Geometry: Points, Lines and Angles

• ##### Author 9-12

60 Minutes

• ##### Device
• TI-89 / TI-89 Titanium
• TI-92 Plus / Voyage™ 200

TI Connect™

• ##### Accessories

TI Connectivity Cable

• ##### Other Materials
This is Activity 9 from the EXPLORATIONS Book:
Geometric Investigations on the Voyage 200 with Cabri

## Investigating Properties of Lines in the Plane

#### Activity Overview

In this activity, students draw a line and determine its slope. They understand that the slope of a line is actually the ratio of rise over run.

#### Before the Activity

• See the attached PDF file for detailed instructions for this activity
• Print page 47 from the attached PDF file for your class
• #### During the Activity

Distribute the page to the class.

• Display the axes and draw a line from the third quadrant to the first quadrant, passing through the origin
• Construct two points on the line in quadrant I, and label them A and C
• Construct a line parallel to the x-axis through A and a line parallel to the y-axis through C
• Label the point of intersection of the lines as B
• Construct and measure segments AB and BC, and compute the ratio (BC)/(AB)
• Understand that this ratio of change in y-coordinate to change in x-coordinate is called the slope of the line
• Move A and C along the line and observe that the slope of a line remains constant at all points
• Determine the equation of the line, and observe that as the line is rotated around the origin, the slope of the line is equal to the coefficient of x in the equation
• Understand that the y-coordinate of a point on a line is the product of the x-coordinate and the slope
• #### After the Activity

Review student results:

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