


Linear Equations and GraphsParallel and Perpendicular LinesT wo lines are parallel if they have the same slope. Parallel lines never intersect. The lines shown below are parallel 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 m_{1} and m_{2} are perpendicular if m_{1}×m_{2} = 1. (Click here to see details.) Hence the slopes are negative reciprocals. That is m_{1} = 1/m_{2}. Exercise 9.<< Linear Equations  Linear Equations and Graphs Index 
