Massey logo
Home > College of Sciences > Institute of Fundamental Sciences >
Maths First > Online Maths Help > Algebra > Linear Equations and Graphs > Parallel and Perpendicular Lines
MathsFirst logo College of Science Brandstrip
  Home  |  Study  |  Research  |  Extramural  |  Campuses  |  Colleges  |  About Massey  |  Library  |  Fees  |  Enrolment


Linear Equations and Graphs

Parallel and Perpendicular Lines

T wo lines are parallel if they have the same slope. Parallel lines never intersect. The lines shown below are parallel

Paralles lines of slope m.

The lines y = 4x, y = 4x + 5 and y = 4x - 100 are also parallel as they all have slope 4.


Perpendicular lines are lines that intersect at right angles (90 degrees). By using Pythagoras’s Theorem it can be shown that two lines with slopes m1 and m2 are perpendicular if  m1×m2 = -1. (Click here to see details.) Hence the slopes are negative reciprocals. That is m1 = -1/m2.

Parallel lines have equal slopes, m1 = m2. Perpendicular lines have negative reciprocal slopes, m1 = -1/m2.

Exercise 9.


Find the slope of the two lines:

x + y =
(2 d.p.)
x + y =
(2 d.p.)


Click on the correct button below for the two lines above:



<< Linear Equations | Linear Equations and Graphs Index |


   Contact Us | About Massey University | Sitemap | Disclaimer | Last updated: November 21, 2012     © Massey University 2003