Right angle

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

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

[edit] See also

[edit] References

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