Year 7 Interactive Maths - Second Edition

## Calculating the Size of Angles

We will next consider adjacent angles, supplementary angles, complementary angles, vertically opposite angles and angles forming a circle.

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

###### Remember:

The sum of adjacent angles forming a straight line is 180º.  Two such angles are also known as supplementary adjacent angles.

Supplementary angles are introduced below.

#### Example 3

Use the information given in the diagram to find x.

##### Solution:

So, the value of x is 136º.

#### Example 4

Use the information given in the diagram to find x.

##### Solution:

So, the value of x is 18°.

### Supplementary Angles

If the sum of two angles adds up to 180°, then the angles are said to be supplementary.

The supplement of 40º is 140º.
The supplement of 140º is 40º.

### Complementary Angles

If the sum of two angles adds up to 90°, then the angles are said to be complementary.

The complement of 55° is 35°.
The complement of 35° is 55°.

#### Example 5

What is the complement of 38°?

## 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 6

What is the supplement of 38°?