Right angle

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An example of modern architecture, designed with many right angles.

In geometry and trigonometry, a right angle is an angle of 90 degrees, corresponding to a quarter turn (that is, a quarter of a full circle). It can be defined as the angle such that twice that angle amounts to a half turn, or 180° ^[1].

Lines that are at a right angle to each other are perpendicular, an important geometrical property. The presence of a right angle in a triangle is the defining factor for right triangles.

A right angle may be expressed in different units:

• 90°
• ^π/₂ radians
• 100 grad (also called grade, gradian, or gon)
• 8 points (of a 32-point compass rose)
• 6 hours (astronomical hour angle)
• ∞% grade on the tangent scale
• 100% grade on the sine scale.

In mathematics, right angle can be an additional unit of angle^[2]. 1r=90°=^π/₂ rad=100^g

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

See also

• Angle: Types of angles
• Orthogonality
• Perpendicular
• Cartesian coordinate system
• Rectangle

References

1. ^ Lindahl, G. (1987). Euklides Geometri. Stockholm, Natur och kultur: ISBN 91-27-72185-X
2. ^ * convertworld.com angles