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In this activity, we will learn how to estimate the size of each angle.
Remember:
Acute angles are smaller than 90°
Right angles are exactly 90°
Obtuse angles are larger than 90°
Reflex angles are larger than 180°
Let's try an example.
Example
Estimate the size of this angle.
Think of key angles such as: 30°, 60°, 90°, 120° and 180°
A right angle is 90°, so 30° is a third of a right angle and 60° is two thirds of a right angle.
A straight line is 180°, so 120° is a right angle plus a third of a right angle.
Answer
The angle is about one third more than a right angle
The angle is about 120°
Using a protractor, we would find that the exact size of this angle = 116°
Are you ready to have a go at some of these yourself now?
