# 11.04 Angles on a straight line

Lesson

## Ideas

Being able to  identify an angle  can help us in this lesson. Let's try this problem to review.

### Examples

#### Example 1

Select the obtuse angle:

A
B
C
D
Worked Solution
Create a strategy

Rotate each angle so that one arm lies over the start.

Apply the idea

Idea summary

A full revolution is made up of 360 degrees, a single degree is written 1\degree.

## Angles on straight lines

### Examples

#### Example 2

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.

### Outcomes

#### VCMMG231

Investigate with and without digital technologies, angles on a straight line, angles at a point and vertically opposite angles. Use results to find unknown angles.