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What Is a Right Angle? (Mathematics Lesson)

What Is a Right Angle?

A right angle is an angle of 90°.

A right angle is a quarter of a revolution.



Note: Right angles are often denoted by adding a small right angle that forms a square with the angle.

Real Examples of Right Angles

The angles below are all right angles:

A Real Example of a Right Angle: The Right Triangle

A right triangle is a triangle containing a right angle.



The right triangle is one of the most useful triangles in mathematics.

It is used for Pythagoras' theorem and in trigonometry.

Read more about right triangles

Complementary Angles

Two angles are complementary if they add up to a right angle.



Read more about complementary angles

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Note

EUCLID AND RIGHT ANGLES

Euclid defines 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".



Lines that are at a right angle to each other are called perpendicular.

OTHER TYPES OF ANGLES

Right angles are one type of angle, the other types are acute, obtuse, straight, reflex and full.