## ::Right angle

### ::concepts

Angle::right Angles::books Right::euclid Triangle::units Theorem::which Geometry::thumb

{{#invoke:Hatnote|hatnote}}

In geometry and trigonometry, a **right angle** is an angle that bisects the angle formed by two halves of a straight line. More precisely, if a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles.<ref>Wentworth p. 8</ref> As a rotation, a right angle corresponds to a quarter turn (that is, a quarter of a full circle).<ref>Wentworth p. 11</ref>

Closely related and important geometrical concepts are perpendicular lines, meaning lines that form right angles at their point of intersection, and orthogonality, which is the property of forming right angles, usually applied to vectors. The presence of a right angle in a triangle is the defining factor for right triangles,<ref>Wentworth p. 40</ref> making the right angles basic to trigonometry.

The term is a calque of Latin *angulus rectus*; here *rectus* means "upright", referring to the vertical perpendicular to a horizontal base line.

**Right angle sections**

Intro Symbols Euclid Conversion to other units Rule of 3-4-5 Thales' theorem See also References

PREVIOUS: Intro | NEXT: Symbols |

<< | >> |