What you need to know
Things to remember:
- Compare the angle you have to a right angle and straight line
- Remember the types of angle above
We start with two important angles, 90 degrees and 180 degrees. These have special names.
The right angle.
The right angle is exactly 90° and is shown with a little square.
The straight line.
The angle of a straight line is exactly 180°
We have three other types of angles, which we define using the right angle and straight line.
The acute angle
It is between 0° and 90° (smaller than a right angle)
The obtuse angle
It is between 90° and 180°
(Between a right angle and straight line)
The reflex angle
It is between 180° and 360°
(Between a straight line and full turn)
Question 1: Which triangle angle is the right angle?
Angle A is the right angle.
Question 2: Which angle is the reflex angle?
Angle C is the reflex angle.