Teaching Algebra with Manipulatives

Demonstration 2
Finding Slope: Zero, Undefined
• Place a coordinate grid transparency on the screen.
• Ask students how to graph the line y 3. Graph a line
through all points where y 3; the line will be parallel to
the x-axis. Graph y 3.
• Ask students to name two points on the line.
Answers will vary.
• Have students find the slope of the line. 0
• Ask whether the slope would be different for any other
line parallel to the x-axis. no
Using Overhead Manipulatives
y
O
x
Algebra 1—Chapter 5
• Ask students how to graph the line x 2. Graph a line
through all points where x 2; the line will be parallel to
the y-axis. Graph x 2.
• Ask students to name two points on the line.
Answers will vary.
• Ask students to find the slope of the line.
The slope of the line x 2 is undefined.
• Ask whether the slope would be undefined for any line
parallel to the y-axis and why. Yes; since the value of x
is constant, the change in x will be 0 for any value of x.
O
y
x
© Glencoe/McGraw-Hill 97 Teaching Algebra with Manipulatives