New
New
Year 5

Angles in triangles

I know that the angles in a triangle sum to 180°.

New
New
Year 5

Angles in triangles

I know that the angles in a triangle sum to 180°.

Lesson details

Key learning points

  1. Angles on a straight line sum to 180 degrees.
  2. Interior angles in triangles sum to 180 degrees.
  3. Missing angles can be calculated using the sum of 180 degrees.

Keywords

  • Quadrilateral - A quadrilateral is a polygon with four straight sides and four vertices.

  • Triangle - A triangle is a polygon with three straight sides and three vertices.

  • Sum - The sum is the result of adding two or more numbers.

Common misconception

Pupils struggle to remember the number of degrees in a triangle as they only know it as a disconnected fact.

Apply pupils' knowledge of angles in a quadrilateral to understanding the sum of the angles in a triangle. Spend time showing how a quadrilateral is constructed using triangles and what happens to the angles as the quadrilateral is partitioned.

It is important that pupils are provided with opportunities to construct triangles for themselves. Using angle tools to help construct triangles is an appropriate step to make use of before moving to drawing angles with a protractor in later lessons.
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).

Lesson video

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6 Questions

Q1.
Look at the hands on this clock face and the arrow. The angle formed is __________.
An image in a quiz
Correct answer: acute
a right angle
obtuse
reflex
Q2.
This triangle has three equal sides and three equal vertices. Select the correct name for this triangle.
An image in a quiz
Correct answer: Equilateral triangle
Isosceles triangle
Scalene triangle
Q3.
Match the angles to the correct description
An image in a quiz
Correct Answer:Smallest angle ,A

A

Correct Answer:Second largest angle ,B

B

Correct Answer:Third largest angle,C

C

Correct Answer:Largest angle,D

D

Q4.
The image is not to scale. What is the value of missing angle a? a = °
An image in a quiz
Correct Answer: 106
Q5.
The image is not to scale. What is the value of missing angle a? a = °
An image in a quiz
Correct Answer: 42
Q6.
The image is not to scale. What is the value of missing angle a? a = °
An image in a quiz
Correct Answer: 197

6 Questions

Q1.
The internal angles in all triangles sum to ___.
90°
Correct answer: 180°
360°
Q2.
Tick the expressions that could represent the angles in a triangle.
Correct answer: 90°+ 25° + 65°
90°+ 30° + 30°
Correct answer: 90°+ 40° + 50°
90°+ 90°
Q3.
Tick the expressions that could represent the angles in a triangle.
75°+ 45° + 45°
Correct answer: 70°+ 10° + 100°
Correct answer: 60°+ 60° + 60°
50°+ 48° + 42°
Q4.
Finish the expression so that it could represent the angle sum of a triangle. 60°+ 75° + °
Correct Answer: 45
Q5.
The image is not to scale. Calculate missing angle a. A = °
An image in a quiz
Correct Answer: 23
Q6.
The image is not to scale. Calculate missing angle a. A = °
An image in a quiz
Correct Answer: 50