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 AnglesThe angles below are all right angles:
A Real Example of a Right Angle: The Right TriangleA 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 AnglesTwo angles are complementary if they add up to a right angle.
Read more about complementary angles
EUCLID AND RIGHT ANGLESEuclid 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.