Acute Angles
An acute angle is an angle of less than 90°.
Right Angles
A
right angle is an angle of 90°.
Don't forget: Right angles are often denoted by adding a small right angle that forms a square with the angle.
Obtuse Angles
An obtuse angle is an angle greater than 90° and less than 180°.
An angle is created by two rays that have a common end point, called the vertex.
Who Classified Angles?
Euclid classified angles in his book, Elements.
Definition 10: "When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right".
Definition 11: "An obtuse angle is an angle greater than a right angle".
Definition 12: "An acute angle is an angle less than a right angle".
Oblique Angles
Acute and obtuse angles are also oblique angles. Oblique angles are neither right angles nor multiples of right angles.
Worksheet
This test is printable and sendable
Interactive Widget
Use this interactive widget to learn about the types of angles. Start by clicking in the shaded area.