# Right angle

A right angle is an angle that measures 90 degrees.

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.

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.

## 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.

A right triangle contains one right angle

The Cartesian Coordinate System is also known as the rectangular coordinate system because of the right angles formed by the axes and grid lines.

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.

See also acute, angle, obtuse, straight angle.