Myths about teaching can hold you back
- Year 8
Using the sum of the interior angles of a triangle
I can use the fact that the interior angles of any triangle sum to 180° to find the size of missing angles.
- Year 8
Using the sum of the interior angles of a triangle
I can use the fact that the interior angles of any triangle sum to 180° to find the size of missing angles.
Lesson details
Key learning points
- Missing angles in triangles can be found using the angle sum.
- Missing angles in triangles can be found using the angle sum and other triangle properties.
Keywords
Interior angle - an angle formed inside a polygon by two of its edges.
Sum - the total when numbers are added together.
Common misconception
Assuming triangles are certain types because of how they look.
Unless there is notation or it has stated the type of triangle you cannot assume.
To help you plan your year 8 maths lesson on: Using the sum of the interior angles of a triangle, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 8 maths lesson on: Using the sum of the interior angles of a triangle, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 maths lessons from the Geometrical properties: polygons unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.The sum of 241, 68 and 192 is .
Q2.Simplify the following expression $$3x+5y-2x+9y+3x+12$$.
Q3.A triangle DEF, where DE = 23 cm, DF = 23 cm and angle EDF is 45° is __________ triangle.
Q4.Solve $$29=54-2x$$
Q5.Which of these are correct for the size of the angle marked $$n$$?

Q6.Select the statements that best complete the following sentence. By tearing the corners off of a triangle and arranging them together at a point it you have...

Assessment exit quiz
6 Questions
Q1.The size of the angle $$x$$° is °.

Q2.Match the two angles of a triangle with its third angle.
60°, 60° -
60°
57°, 103° -
20°
90°, 27° -
63°
108°, 51° -
21°
51°, 98° -
31°
104°, 38° -
38°
Q3.In which of these triangles is there enough information for you to calculate the size of the missing angle?




Q4.The size of the angle $$x°$$ is °.

Q5.Which of the following are calculations to find the value of $$y$$?

Q6.Work out the value of $$m$$.
