Angles - Foundation
There are 360° in a complete turn. So in half a turn there are 180°, and in a quarter of a turn 90°.
We sometimes call a quarter of a turn a right angle, and mark it with a square.
We can use these facts to solve simple problems. Here are some examples:
Find angle a in this diagram:
The answer is 110°.
All the angles add up to 360° (a complete turn).
So a = 360° - 60° - 100° - 90° = 110°.
Remember that a right angle (90°) can be marked with a square.
Find angle b in this diagram.
The answer is 100°.
The angles make a straight line (half a turn).
So b = 180° - 50° - 30° = 100°.
Find angle c in this diagram.
The answer is 70°.
The two angles make a right angle.
So c = 90° - 20° = 70°
For your exam, you will need to know the following types of angle:
Any angle that is less than 90° is called an acute angle.
Any angle which is between 90° and 180° is called an obtuse angle.
Any angle that is between 180° and 360° is called a reflex angle.
You also need to remember that the angles in a triangle add up to 180°, and that the angles in a quadrilateral add up to 360°.
p + q + r = 180° w + x + y + Z = 360°