Angles are an important part of mathematics and they play an essential part in geometry.
What is an angle?
An angle measures the amount of turn between two lines (or arms) that are joined at one common endpoint.
The trick is to learn the name of each angle. As the angle increases, the name changes.
Acute Angles
Acute angles are the smallest - between (but not including) zero and 90°.
Right Angles
Right angles measure exactly 90°.
Obtuse Angles
Obtuse angles measure greater than 90° and less than 180°.
Straight Angles
The straight angle measures exactly 180° - basically a straight line.
Reflex Angles
Reflex angles measure greater than 180° and less than 360°.
Full Angles or Full Rotations
This is an angle whose measure is exactly 360° - basically a full circle.
The Difference between Obtuse and Reflex Angles
Pay attention to what angle you are being asked to measure. Even though the lines look the same, the angles are different – an obtuse angle or a reflex angle:
We offer some free worksheets on classifying angles for practice. You can find them here.
