Parallel lines
Two lines are parallel if they always keep the same distance apart, and so never cross — even if you extend them forever in both directions.
Parallel lines are shown with the symbol //: line AB // line CD means "line AB is parallel to line CD".
Perpendicular lines
Two lines are perpendicular if they cross forming exactly a right angle (90°). Perpendicularity is shown with the symbol ⊥: AB ⊥ CD.
Intersecting lines
Two lines are intersecting as soon as they cross at a single point, whatever angle is formed there. It's the broadest category: two lines that aren't parallel are necessarily intersecting.
Checking with a ruler and set square
- To check if two lines are parallel: measure the gap between them at two or three different spots with a ruler — if the gap is always the same, they're parallel.
- To check if two lines are perpendicular: place a set square at the point where they cross — if both edges of the set square line up perfectly with the two lines, they're perpendicular.
Where to spot them around you
- Parallel: the lines on a page of paper, the rungs of a ladder, railway tracks.
- Perpendicular: the sides of a door, a cross shape, the corner of a table.
- Intersecting (without being perpendicular): the arms of a big tilted X, two roads that cross at an angle.
Mistakes to avoid
- Thinking that all intersecting lines are perpendicular — only the ones that form a right angle are.
- Judging "by eye" without checking with a ruler or set square — two lines that look parallel can have a tiny gap that grows if extended.
- Mixing up the symbols // (parallel) and ⊥ (perpendicular).
Worked exercises
Two lines cross forming a 90° angle. What are they called?
Two lines keep a gap of 3 cm along their whole length. What can you say?
Two lines cross forming a 60° angle. Are they perpendicular?
Now it's your turn!
On EasyMaths, your child practises recognising parallel, perpendicular and intersecting lines with exercises that never repeat and instant marking.
Start the exercises →Frequently asked questions
How do you recognise parallel lines?
Two lines are parallel if they always keep the same distance apart, never meeting, even if extended forever. You can check this with a ruler and a set square, measuring the gap in several places.
How do you recognise perpendicular lines?
Two lines are perpendicular if they cross forming exactly a right angle (90°). You check this with a set square: if both edges of the set square line up perfectly with the two lines, they're perpendicular.
What are intersecting lines?
Intersecting lines are two lines that cross at a single point, whatever angle is formed. Perpendicular lines are a special case of intersecting lines (ones that cross forming a right angle).