An acute angle is smaller than a right angle. An acute angle is less than 90°. Here are two examples:
One way to remember an acute angle is to think that cute things are usually little. Also, acute means sharp, as in sharp pain.
Obtuse angles are between a right angle and a straight angle; so an obtuse angle is larger than 90°, but smaller than 180°. Obtuse is the opposite of sharp – it means dull. Here are two examples:
Reflex angles are larger than 180°, but less than 360°. Here is one example:
We compare angles by looking to see if they are smaller or larger than the types of angles shown above, or by measuring them as shown in the next section.