Primary 3 Perpendicular and Parallel Lines
Learn to recognise perpendicular and parallel lines, then draw both using a set square. Check for a right angle or an equal gap instead of judging only by how lines look on the page.
Keywords
- Perpendicular lines
- Lines that meet at a right angle of 90°.
- Parallel lines
- Lines that stay the same distance apart and never meet, even if extended.
- Set square
- A triangular drawing tool with a right-angle corner.
Perpendicular and parallel lines
Perpendicular lines meet to form a right angle of 90°, shown by a small square at the intersection. Parallel lines stay the same distance apart and never meet, even when extended. Both relationships stay the same if the page is turned.
Compare the two relationships
Perpendicular lines
Meet at a right angle (90°).
Parallel lines
Stay the same distance apart. No intersection: They continue forever without ever meeting.
See worked example
Look at a rectangular book cover. How are adjacent edges related, and how are opposite edges related?
- Adjacent edges meet at a square corner, so they form a right angle.
- Opposite edges stay the same distance apart along the cover.
- Name each relationship from its test.
Answer: Adjacent edges are perpendicular. Opposite edges are parallel.
Try together
Two short lines do not touch, but their gap narrows from left to right. Are they parallel?
Reveal the answer
No. Their gap changes, so the lines would meet if extended.
Drawing perpendicular and parallel lines with a set square
Use the 90° corner of a set square to draw a perpendicular line to a given line. To draw a parallel line, hold a ruler steady against the set square, slide the set square along the ruler without turning it, and draw along the same edge in its new position.
Draw with a set square
See worked example
How can you draw a line perpendicular to a given straight line?
- Place one edge of the set square's right-angle corner along the given line.
- Keep the set square still and draw along the other edge of the right-angle corner.
- Mark the 90° angle with a small square at the meeting point.
Answer: The new line is perpendicular to the given line.
Try together
How can you use a set square and a ruler to draw a line parallel to a given line?
Reveal the answer
Draw the first line along one set-square edge. Hold a ruler against another edge, slide the set square along the ruler without turning it, and draw the second line along the same edge.