# Use the area of a triangle to calculate unknown measurements

I can calculate unknown dimensions of a triangle with a specified area.

# Use the area of a triangle to calculate unknown measurements

I can calculate unknown dimensions of a triangle with a specified area.

## Lesson details

### Key learning points

- The area of a triangle is half the area of a parallelogram with the same perpendicular base and height.
- The area of a triangle can be calculated using the formula area = base × perpendicular height ÷ 2
- A missing perpendicular height in a triangle can be found using the formula area × 2 ÷ base
- A missing base in a triangle can be found using the formula area × 2 ÷ perpendicular height

### Common misconception

When drawing triangles with a given area pupils may create a factor pair of the triangle's area when drawing the base and perpendicular height. The factor pair refers to the surrounding parallelogram.

For pupils who are making this mistake, encourage them to sketch the parallelogram around the triangle, reminding them to double the triangle area before finding the factor pairs.

### Keywords

Base - The base is the side which is perpendicular to the shape’s height.

Perpendicular - Two lines are perpendicular if they meet at a right angle.

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Video

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