11.07 Angles at a point

Lesson

Are you ready?

Can you work out the value of an  angle on a straight line  ?

Examples

Example 1

Find the size of the missing angle.

Worked Solution
Create a strategy

Subtract the given angle from 180\degree.

Apply the idea

The two angles should add up to 180\degree since they lie on a straight line. So to find the missing angle we can subtract 129\degree from 180\degree .

Idea summary

Angles on a straight line always add up to 180 degrees.

Angles at a point

This video looks at angles at a point, and how to use a full revolution being equal to 360 degrees to answer problems.

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Examples

Example 2

Find the size of the missing angle.

Worked Solution
Create a strategy

Add the given angles and subtract the sum from 360\degree, which is the angle in a revolution.

Apply the idea

The three angles should add to 360\degree since they make up a revolution. So if we add up the given angles and subtract them from 360\degree , we will find the unknown angle.

Idea summary

It doesn't matter how many angles are formed at a point, the sum is always 360 degrees.

Outcomes

MA3-16MG

measures and constructs angles, and applies angle relationships to find unknown angles