Editing Right angle (section)

{{short description|90° angle (π/2 radians)}}
{{Other uses}}
[[Image:Right angle.svg|thumb|134px|A right angle is equal to 90 degrees.]]
[[Image:Perpendicular-coloured.svg|right|thumb|A line segment (AB) drawn so that it forms right angles with a line (CD)]]
{{Angles}}

In [[geometry]] and [[trigonometry]], a '''right angle''' is an [[angle]] of exactly 90 [[Degree (angle)|degrees]] or {{sfrac|<math>\pi</math>|2}} [[radian]]s<ref>{{cite web|title=Right Angle|url=http://www.mathopenref.com/angleright.html|website=Math Open Reference|access-date=26 April 2017}}</ref> corresponding to a quarter [[turn (geometry)|turn]].<ref>Wentworth p. 11</ref> If a [[Line (mathematics)#Ray|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> The term is a [[calque]] of [[Latin]] ''angulus rectus''; here ''rectus'' means "upright", referring to the vertical perpendicular to a horizontal base line.

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 [[Euclidean vector|vectors]]. The presence of a right angle in a [[triangle]] is the defining factor for [[right triangle]]s,<ref>Wentworth p. 40</ref> making the right angle basic to trigonometry.