## ::Right angle

### ::concepts

Angle::right    Angles::books    Right::euclid    Triangle::units    Theorem::which    Geometry::thumb

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A right angle is equal to 90 degrees.
A line segment (AB) drawn so that it forms right angles with a line (CD).

In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two halves of a straight line. More precisely, if a 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> As a rotation, a right angle corresponds to a quarter turn (that is, a quarter of a full circle).<ref>Wentworth p. 11</ref>

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 vectors. The presence of a right angle in a triangle is the defining factor for right triangles,<ref>Wentworth p. 40</ref> making the right angles basic to trigonometry.

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

Right angle sections
Intro   Symbols    Euclid    Conversion to other units    Rule of 3-4-5    Thales' theorem    See also    References

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