Year 9 Interactive Maths - Second Edition

Angle Facts of Geometry

Adjacent Angles

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

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?

Solution:

Example 2

What is the supplement of 35º?

Solution:

Example 3

Use the information given in the diagram to find x.

So, the value of x is 133.

Example 4

Use the information given in the diagram to find x.

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.

Key Terms

adjacent angles, adjacent angles forming a straight line, supplementary angles, complementary angles, angles at a point