Oak National Academy
Oak National Academy
Teachers
Pupils
New
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
Share function coming soon...
New
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
Share function coming soon...

Slide deck

Download slide deck

Lesson details

Key learning points

  1. 0.5 x base x perpendicular height can be used to find the area of any triangle.
  2. Missing sides can be found if the area is known.

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.

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.

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).

Video

Loading...

Worksheet

Download worksheet

Starter quiz

Download starter quiz

6 Questions

Q1.
The perpendicular is the perpendicular distance from the base to the opposite vertex.
Correct Answer: height
Q2.
True or false? You can calculate the area of this triangle.
An image in a quiz
Correct answer: True
False
Q3.
Calculate the area of the triangle.
An image in a quiz
27 cm$$^2$$
Correct answer: 90 cm$$^2$$
180 cm$$^2$$
360 cm$$^2$$
Q4.
Calculate the area of a triangle with a base of 13 cm and a perpendicular height of 3 cm (you do not need to give the units).
Correct Answer: 19.5 cm$$^2$$, 19.5
Q5.
Two triangles can always be placed together to create a parallelogram.
Correct Answer: identical, congruent
Q6.
Which of these is the correct way to calculate the area of this triangle?
An image in a quiz
base $$\times$$ perpendicular height $$\times$$ 0.2
base $$\times$$ perpendicular height $$\div {1 \over 2}$$
Correct answer: $$b \times h \times {1 \over 2}$$
$$bh \times 2$$

Exit quiz

Download exit quiz

6 Questions

Q1.
The base and height of this triangle measure:
An image in a quiz
13.3 mm and 15.3 mm
Correct answer: 15.3 mm and 18.3 mm
13.3 mm and 18.3 mm
13.3 mm and 19.3 mm
Q2.
Select the correct expression for the area of the triangle.
An image in a quiz
Correct answer: $$ac \over 2$$
$$ab \over 2$$
$$bc \over 2$$
Q3.
Select the correct expression for the area of the triangle.
An image in a quiz
$$28bd \over 2$$
$$20bd^{2}t \over 2$$
Correct answer: $$35dt \over 2$$
Q4.
Calculate the missing side length.
An image in a quiz
Correct Answer: 10 cm, 10
Q5.
Calculate the missing side length.
An image in a quiz
Correct Answer: 3.3 cm, 3.3
Q6.
Calculate the missing side length.
An image in a quiz
Correct Answer: 2.5 cm, 2.5