Right angle

90° angle (π/2 radians)

In geometry and trigonometry, a right angle is an angle of exactly 90 degrees or ⁠ π {\displaystyle \pi } /2⁠ radians corresponding to a quarter turn. If a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles. The term is a calque of Latin angulus rectus; here rectus means "upright", referring to the vertical perpendicular to a horizontal base line.

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