Right angle
A right angle is an angle that measures 90 degrees.
![](/img/a/geometry/angles/right/right-angle.png)
In geometry, a square is typically drawn at the vertex of an angle to indicate it is a right angle.
Lines and planes
If the intersection of two lines forms a right angle, the lines are said to be perpendicular.
![](/img/a/geometry/angles/right/perpendicular-lines.png)
If a plane contains a line that intersects another plane at a right angle, it is perpendicular to that plane. Any plane containing a line meeting another plane at a right angle is also perpendicular to that plane. We say that planes and lines that meet each other at right angles are orthogonal.
![](/img/a/geometry/angles/right/line-plane.png)
![](/img/a/geometry/angles/right/line-planes.png)
Right angles in geometry
Right angles are used widely in geometry. The following are some geometric objects or situations that involve the use of right angles.
A square and rectangle contain four right angles.
![](/img/a/geometry/angles/right/square-rectangle.png)
A right triangle contains one right angle
![](/img/a/geometry/angles/right/right-triangle.png)
The Cartesian Coordinate System is also known as the rectangular coordinate system because of the right angles formed by the axes and grid lines.
![](/img/a/geometry/angles/right/coordinate-plane.png)
The Cartesian Coordinate System above is a two-dimensional plane where the x-axis and y-axis meet at a right angle at what is called the origin. Also, each horizontal line in the grid intersects each vertical line in the grid at a right angle.
A line tangent to a circle forms a right angle with the circle's radius, containing the point of tangency.
![](/img/a/geometry/angles/right/circle-tangent-line.png)
See also acute, angle, obtuse, straight angle.