# Right Angles(KS2, Year 6)

homesitemapgeometryright angles
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.

## Dictionary Definition

The Oxford English Dictionary defines a right angle as "an angle of ninety degrees; specifically one formed by two perpendicular lines, as in the corner of a square."

## 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. Learn more about right triangles

## 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.

## Complementary Angles

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

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