Using the formula for the area of a triangle

You can use the formula for the area of a triangle to calculate missing side lengths.

Download all resources

Share activities with pupils

New

Year 7

Using the formula for the area of a triangle

You can use the formula for the area of a triangle to calculate missing side lengths.

Download all resources

Share activities with pupils

These resources will be removed by end of Summer Term 2025.

Switch to our new teaching resources now - designed by teachers and leading subject experts, and tested in classrooms.

View new resources

Slide deck

Download slide deck

Skip slide deck

Lesson details

Key learning points

0.5 x base x perpendicular height can be used to find the area of any triangle.
Missing sides can be found if the area is known.

Keywords

Base - The base is the side which is perpendicular to the height.
Perpendicular height - The perpendicular height is the perpendicular distance from the base to the opposite vertex.

Common misconception

Pupils may think the height of the triangle is the slanted height rather than perpendicular.

The base and height to be used must be perpendicular (at a right angle) to each other.

If pupils are not ready to use algebra within this topic, use the correct mathematical terms for the unknown sides alongside the algebra to support their understanding of what the letter represents.

Teacher tip

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).