The different types of angles
Let's start with the right angle. Two perpendicular half lines form a right angle. This angle is important because it allows us to name the other angles. A right angle is an angle of 90 degrees.
An angle smaller than a right angle is called acute angle.
An angle larger than a right angle is called obtuse angle.
When two half lines are on the same line, they form a straight angle. A straight angle is 180 degrees and it's the double of a right angle.
When the two arms of the angle coincide, you can see an internal angle and an external angle:
- a zero angle is 0 degrees;
- a full angle is 360 degrees.