Education Technology

Y-Intercept Exploration & Writing Equations of Lines

Published on 05/31/2007

Activity Overview

Using TI-Navigator, students will discover the effect of 'b' on the graph of y = mx + b. Subsequently, they will learn to write the equation of a line in slope-intercept form.

Before the Activity

Students should have pre-requisite knowledge of y = kx graphs and have discussed slope to the point that y = mx graphs are well understood. Configure the Activity Center to allow students to send in one equation, let students view graphs of equations, and send current graph contents as background. Place the equation y = 2x + 3 on graph. Make sure you are on the 'Graph' tab so that the equation cannot be seen on the Activity Center screen.

During the Activity

Part 1: Have students log in to TI-Navigator. Send out a Quick Poll that asks, True or False: In y = mx + b, 'b' will always cause the graph to 'move up'. As a class, look at student responses. Do not confirm or deny the correctness of the class's response at this point. Ask students to exit the Navigator application and type an equation in Y= of the form y = mx + b. Then, they should GRAPH the line. Have students TRACE (so that the equation will show on the screen with the graph). Do a Screen Capture. Discuss any patterns seen. If no one chooses a negative constant for b or a number other than an integer, you will want to ask students to change their equation accordingly and do another screen capture. Continue the class discussion. Conclude with what effect the constant, b, in the y = mx + b equation has on the graph. Return to Quick Poll results and ask students why FALSE was the correct answer. Part 2: Ask students to go back into Navigator and select Activity Center. Start the activity. Have students send an equation of a graph with the same y-intercept as the graph on their scren. Go to the 'Graph-Equation Tab'. Discuss the various graphs that were contributed. Make sure students understand that the constant must be 3 in order to go through the y-intercept of the given graph. Go to 'Edit' in Activity Center and 'Clear Activity Data'. Make sure you are on the 'graph' tab. Ask students to contribute an equation of a line with slope of '3 and y-intercept of 4. Start the activity. After students have contributed, discuss the fact that there is only one line on the screen. If there is more than one line (which there will most likely be) on the screen, show 'Graph-Equation' and look at the unlike equations. Discuss how someone could have made that error in writing their equation. Continue clearing the data and sending out the activity as necessary.

After the Activity

Assess students? understanding by sending out the quick Learn Check provided here or a similar one. Collect student answers and use Class Analysis slide show to review the results with the students and provide any needed clarification on the concept.