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Year 9 Interactive Maths - Second Edition


Angle Facts of Geometry

The purpose of this section is to revise 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 180.


Supplementary Angles

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

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


Complementary Angles

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

 

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


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 40?

Solution:

 

 

 



Example 2

What is the supplement of 35?

Solution:

 

 

 



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.


Key Terms

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


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