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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.

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New

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.

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Share activities with pupils

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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.

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.

Keywords

Interior angle - an angle formed inside a polygon by two of its edges.
Sum - the total when numbers are added together.

Pupils could create their own problems for peers. They may wish to look at combining triangles to make the problems more challenging.

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).

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Starter quiz

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6 Questions

Q1.

The sum of 241, 68 and 192 is .

Correct Answer: 501, five hundred and one

Q2.

Simplify the following expression $$3x+5y-2x+9y+3x+12$$.

$$8x+14y+12$$

$$8x-14y+12$$

Correct answer: $$4x+14y+12$$

$$4x-14y+12$$

$$18xy+12$$

Q3.

A triangle DEF, where DE = 23 cm, DF = 23 cm and angle EDF is 45° is __________ triangle.

a scalene

Correct answer: an isosceles

an equilateral

a right-angled scalene

a right-angled isosceles

Q4.

Solve $$29=54-2x$$

Correct answer: $$x=12.5$$

$$x=-12.5$$

$$x=41.5$$

$$x=83$$

$$x=25$$

Q5.

Which of these are correct for the size of the angle marked $$n$$?

$$n=28$$

Correct answer: $$n=180-(28+131)$$

$$n=131$$

Correct answer: $$n=180-28-131$$

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...