Skip to content
Oak National Academy
Oak National Academy
Teachers
Pupils
icon-background-square
New
New
Year 8

Diagonals of a rhombus

I can appreciate that the diagonals of a rhombus bisect one another at right angles and the angles are bisected.

Download all resources
arrow-right
Share activities with pupils
arrow-right
icon-background-square
New
New
Year 8

Diagonals of a rhombus

I can appreciate that the diagonals of a rhombus bisect one another at right angles and the angles are bisected.

Download all resources
arrow-right
Share activities with pupils
arrow-right
warning

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.

These resources were created for remote use during the pandemic and are not designed for classroom teaching.

View new resources
arrow-right

Lesson details

Key learning points

  1. An isosceles triangle has a line of symmetry that splits it into two congruent triangles.
  2. In a rhombus each diagonal splits the rhombus into two congruent isosceles triangles bisecting the angles.
  3. The two diagonals meet at right angles.
  4. The two diagonals bisect each other.

Keywords

  • Bisect - To bisect means to cut or divide an object into two equal parts.

  • Altitude - The altitude of a triangle is a line segment from a vertex of a triangle to the opposite edge. It is perpendicular to that edge.

Common misconception

Pupils may struggle with a diagonal of a shape being vertical or horizontal.

By reminding pupils of the definition, ask them to check if it fits and the shape could be rotated as well.


To help you plan your year 8 maths lesson on: Diagonals of a rhombus, download all teaching resources for free and adapt to suit your pupils' needs...

You can set up pair or group work to explore the question 'Is a square a rhombus?' Pupils will need to use good mathematical vocabulary and reasoning to explain their argument. Then you could have them consider 'is a rhombus a square?'.
speech-bubble
Teacher tip
copyright

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

Skip lesson video

Loading...

Starter quiz

Download starter quiz

6 Questions

Q1.
If two lines are perpendicular to each other then they create a $$^\circ$$ angle.
Correct Answer: 90 , ninety
Q2.
Match the type of triangle to the interior angles.
Correct Answer:Scalene triangle,74°, 36° and 70°
tick

74°, 36° and 70°

Correct Answer:Isosceles triangle,28°, 124° and 28°
tick

28°, 124° and 28°

Correct Answer:Right-angled triangle,30°, 60° and 90°
tick

30°, 60° and 90°

Correct Answer:Equilateral triangle,60°, 60° and 60°
tick

60°, 60° and 60°

Q3.
How many lines of symmetry does a rhombus have?
0
1
Correct answer: 2
3
4
Q4.
The missing angle in this triangle is °.
An image in a quiz
Correct Answer: 47, forty seven
Q5.
Select all of the properties of a rhombus.
It has three equal edges.
Correct answer: It has equal edges.
Correct answer: It has four interior angles.
It has one set of parallel sides.
Correct answer: Opposite angles are equal.
Q6.
Which of these is not a construction of a rhombus?
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz

Exit quiz

Download exit quiz

6 Questions

Q1.
To means to cut or divide an object into two equal parts.
Correct Answer: bisect
Q2.
How many of the altitudes of an isosceles are also a line of symmetry?
0
Correct answer: 1
2
3
Q3.
The diagonals of a rhombus ...
Correct answer: ...are perpendicular to each other.
Correct answer: ...bisect each other.
...are always equal in length.
Correct answer: ...bisect the angle they pass through.
...cannot be vertical or horizontal.
Q4.
In this diagram of a rhombus and its diagonals, the angle marked b is °.
An image in a quiz
Correct Answer: 116, one hundred and sixteen
Q5.
Which of the following statements are true about this image?
An image in a quiz
Correct answer: $$a=58+c$$
$$b = a + c$$
$$b=2a$$
Correct answer: $$\frac{b}{2}=58$$
$$b+c=180$$
Q6.
A rhombus has diagonals with lengths of 8 cm and 12 cm. Which of the following calculations will work out the area of the rhombus?
$$2\times\left(\frac{1}{2}\times8\times12\right)$$
Correct answer: $$2\times\left(\frac{1}{2}\times4\times12\right)$$
$$2\times\left(\frac{1}{2}\times4\times6\right)$$
Correct answer: $$4\times\left(\frac{1}{2}\times4\times6\right)$$
Correct answer: $$2\times\left(\frac{1}{2}\times8\times6\right)$$