Two lines are perpendicular if the product of their slopes is -1. Also, the two intersecting lines form right angles.

Determine if y = 2x+5 and x+2y = -2 are perpendicular then graph the equations to check.

Since the product of the slopes is [2*(-1/2)]= -1, the two lines are perpendicular.

Try graphing both equations. Go to the Graph-It applet below. To graph y = 2x+5 and x+2y = -2

Click on Set Graph Set Range to -10, 10 Set Grid Lines to 1 Type in 2 * x+5 for eq. 1 Put a Check in the box next to the function In the next box type in -.5 * x-1 for eq. 2 Put a Check in the box next to the function Note: * must be used when multiplying

Determine if y = x+2 and 4x+2y = 4 are perpendicular then graph the equations to check.

Since the product of the slopes [1 * (-2)] does not equal -1 , the two lines are not perpendicular.

Try graphing both equations. Go to the Graph-It applet below. To graph y = x+2 and 4x+2y = 4

Click on Set Graph Set Range to -10, 10 Set Grid Lines to 1 Type in x+2 for eq. 1 Put a Check in the box next to the function In the next box type in -2 * x+2 for eq. 2 Put a Check in the box next to the function Note: * must be used when multiplying

Quick Hints:

• X is the default domain variable.
• Point to the graph to get exact values.