New
New
Lesson 12 of 15
New
New
- Year 5
Angles in triangles
I know that the angles in a triangle sum to 180°.
Lesson details
Key learning points
- Angles on a straight line sum to 180 degrees.
- Interior angles in triangles sum to 180 degrees.
- 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 (2025), 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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Prior knowledge starter quiz
6 Questions
Q1.Look at the hands on this clock face and the arrow. The angle formed is __________.
Look at the hands on this clock face and the arrow. The angle formed is __________.
a right angle
obtuse
reflex
Q2.This triangle has three equal sides and three equal vertices. Select the correct name for this triangle.
This triangle has three equal sides and three equal vertices. Select the correct name for this triangle.
Isosceles triangle
Scalene triangle
Q3.Match the angles to the correct description
Match the angles to the correct description
Q4.The image is not to scale. What is the value of missing angle a? a = °
The image is not to scale. What is the value of missing angle a? a = °
Q5.The image is not to scale. What is the value of missing angle a? a = °
The image is not to scale. What is the value of missing angle a? a = °
Q6.The image is not to scale. What is the value of missing angle a? a = °
The image is not to scale. What is the value of missing angle a? a = °
Assessment exit quiz
6 Questions
Q1.The internal angles in all triangles sum to ___.
The internal angles in all triangles sum to ___.
90°
360°
Q2.Tick the expressions that could represent the angles in a triangle.
Tick the expressions that could represent the angles in a triangle.
90°+ 30° + 30°
90°+ 90°
Q3.Tick the expressions that could represent the angles in a triangle.
Tick the expressions that could represent the angles in a triangle.
75°+ 45° + 45°
50°+ 48° + 42°
Q4.Finish the expression so that it could represent the angle sum of a triangle. 60°+ 75° + °
Finish the expression so that it could represent the angle sum of a triangle. 60°+ 75° + °
Q5.The image is not to scale. Calculate missing angle a. A = °
The image is not to scale. Calculate missing angle a. A = °
Q6.The image is not to scale. Calculate missing angle a. A = °
The image is not to scale. Calculate missing angle a. A = °
