Year 9 Interactive Maths - Second Edition

## Angle Facts of Geometry

The purpose of this section is to revise angle facts of geometry.

Angles that lie on either side of a common arm are said to be adjacent.

###### Recall that:

The sum of adjacent angles forming a straight line is 180º.

### Supplementary Angles

If the sum of two angles is 180º, then the angles are said to be supplementary.

The supplement of 50º is 130o.
The supplement of 130o is 50o.

### Complementary Angles

If the sum of two angles is 90º, then the angles are said to be complementary.

The complement of 60º is 30º.
The complement of 30º is 60º.

### Method for Finding the Value of a Pronumeral

To find the value of the pronumeral from the given information, write an equation.  Then solve the equation and write the answer in words.

#### Example 1

What is the complement of 40º?

#### Example 2

What is the supplement of 35º?

#### Example 3

Use the information given in the diagram to find x.

##### Solution:

So, the value of x is 133.

#### Example 4

Use the information given in the diagram to find x.

##### Solution:

So, the value of x is 15.

### Angles at a Point

###### Recall that:

The sum of all angles that meet at a point is equal to 360 degrees.

#### Example 5

Use the information given in the diagram to find x.

##### Solution:

So, the value of x is 66.