Year 7 Interactive Maths - Second Edition

Calculating the Size of Angles

Adjacent Angles

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°?

Solution:

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°?

Solution:

Key Terms

adjacent angles, supplementary adjacent angles, supplementary angles, complementary angles