What are perpendicular lines?
Year 3 identifies horizontal and vertical lines and pairs of perpendicular and parallel lines. Below: what it means, a worked example, the mistake to watch for and an 11+ question.
The answer
Perpendicular lines meet or cross at a right angle, which is 90°.
What it means
The corner of a page, a plus sign and the letter T all show perpendicular lines.
In diagrams, a small square in the corner shows that two lines are perpendicular.
A worked example
Are the diagonals of a square perpendicular?
- Draw both diagonals of a square. They cross in the middle.
- All four angles where they cross are right angles, so yes, they are perpendicular.
The common mistake
Thinking perpendicular means vertical. Vertical is a direction, straight up and down. Two sloping lines are perpendicular if they meet at 90°.
How it comes up in the 11+
Which of these capital letters have a pair of perpendicular lines: A, E, H, N, T?
Answer: E, H and T
- E, H and T all have a straight up line meeting a straight across line at 90°.
- A and N are made with sloping lines that do not meet at right angles.
Related words and practice
More maths words
Questions parents ask
What is the difference between perpendicular and parallel?
Perpendicular lines meet at a right angle. Parallel lines never meet at all.
Are horizontal and vertical lines perpendicular?
Yes. A horizontal line and a vertical line always meet at 90°.
Knowing the words is half of an 11+ maths question
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