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)


Example Questions


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.