CK-12 Geometry-Concepts

http://www.ck12.org Chapter 3. Parallel and Perpendicular Lines

First, we have to change each equation into slope-intercept form. In other words, we need to solve each equation for
y.

3 x− 4 y= 8 4 x+ 3 y= 15

− 4 y=− 3 x+ 8 3 y=− 4 x+ 15

y=

3

4

x− 2 y=−

4

3

x+ 5

Now that the lines are in slope-intercept form (also calledy−intercept form), we can tell they are perpendicular
because their slopes are opposite reciprocals.

Watch this video for help with the Examples above.

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/52446

CK-12 Foundation: Chapter3PerpendicularLinesintheCordinatePlaneB

Vocabulary

Two lines in the coordinate plane with slopes that are opposite signs and reciprocals of each other areperpendicular
and intersect at a 90◦, or right, angle.Slopemeasures the steepness of a line.

Guided Practice

1. Determine which of the following pairs of lines are perpendicular.
   
   
   • y=− 2 x+3 andy=^12 x+ 3
   
   
   • y= 4 x−2 andy= 4 x+ 5