A perpendicular with a set square
Draw AB = 7 cm, mark P on it 3 cm from A, and draw the line through P perpendicular to AB.
Draw AB = 8 cm, mark P on it 5 cm from A, and draw the line through P perpendicular to AB.
Draw AB = 6 cm, mark P on it 2 cm from A, and draw the line through P perpendicular to AB.
Draw AB = 9 cm, mark P on it 4.5 cm from A, and draw the line through P perpendicular to AB.
1. Draw AB = 7 cm, and mark P on it, 3 cm from A.
2. Lay a ruler along AB, and hold it firmly.
3. Stand a set square on the ruler, with its right-angled corner at P.
4. Draw a line from P up the set square’s other edge, to Q.
5. Take the set square away: PQ ⊥ AB.
1. Draw AB = 8 cm, and mark P on it, 5 cm from A.
2. Lay a ruler along AB, and hold it firmly.
3. Stand a set square on the ruler, with its right-angled corner at P.
4. Draw a line from P up the set square’s other edge, to Q.
5. Take the set square away: PQ ⊥ AB.
1. Draw AB = 6 cm, and mark P on it, 2 cm from A.
2. Lay a ruler along AB, and hold it firmly.
3. Stand a set square on the ruler, with its right-angled corner at P.
4. Draw a line from P up the set square’s other edge, to Q.
5. Take the set square away: PQ ⊥ AB.
1. Draw AB = 9 cm, and mark P on it, 4.5 cm from A.
2. Lay a ruler along AB, and hold it firmly.
3. Stand a set square on the ruler, with its right-angled corner at P.
4. Draw a line from P up the set square’s other edge, to Q.
5. Take the set square away: PQ ⊥ AB.
Why it works
The corner of a set square between its two short edges is exactly 90°. With one of those edges along AB (the ruler keeps it there), the other edge stands at 90° to AB, so a line drawn along it is perpendicular to AB.