Two special pairs of lines
Straight lines can be related in special ways. Two important pairs are parallel lines and perpendicular lines.
Key idea
Parallel lines stay the same distance apart and never meet. We write // for parallel. Perpendicular lines cross to make a right angle (90°). We write ⊥ for perpendicular.
Spotting them around us
The two long edges of a ruler are parallel, and so are the lines on a page of exercise book paper. The corner of a window or a table, where one edge meets another at 90°, shows perpendicular lines. Look for a right angle: if you can see one, the lines are perpendicular, not parallel.
Worked example
Look at a square. The top and bottom edges never meet, so they are parallel. The left edge meets the bottom edge at 90°, so those two are perpendicular.
Remember
- Parallel: never meet, same gap, symbol //.
- Perpendicular: meet at 90°, symbol ⊥.
- A right angle is the clue for perpendicular.