measurement · Year 6 · Suggested learning sequence
Area of a triangle
Every triangle is half of a rectangle (or parallelogram) with the same base and height. So the area is ½ × base × height. The height must be at right angles to the base: it is the straight-up distance, often drawn as a dashed line. Never use a slanted side as the height. In an obtuse triangle, the height falls outside the shape and the base is extended with a dashed line, but the extension is not part of the base.
Sample questions
This right-angled triangle has a base of 6 cm and a height of 5 cm. What is its area in square centimetres?
- Area of a triangle = ½ × base × height.
- The two sides at the right angle are the base, 6 cm, and the height, 5 cm.
- ½ × 6 × 5 = ½ × 30 = 15 cm².
Answer: 15
This right-angled triangle has a base of 10 cm and a height of 5 cm. What is its area in square centimetres?
- Area of a triangle = ½ × base × height.
- The two sides at the right angle are the base, 10 cm, and the height, 5 cm.
- ½ × 10 × 5 = ½ × 50 = 25 cm².
Answer: 25
This right-angled triangle has a base of 8 cm and a height of 6 cm. What is its area in square centimetres?
- Area of a triangle = ½ × base × height.
- The two sides at the right angle are the base, 8 cm, and the height, 6 cm.
- ½ × 8 × 6 = ½ × 48 = 24 cm².
Answer: 24