## angle
angulus for a sharp bend. Plane angles are measured
in degrees or radians. A right angle has exactly 90° (or π/2 radians), an acute angle less than 90°, an obtuse angle
has between 90° and 180°, and a straight angle has exactly 180°.
Any angle that is at most 180° is said to be convex. An angle between
180° and 360° is called a reflex
angle. An angle of exactly 360° is said to be a full angle. Complementary
angles add to give 90°, supplementary angles make a total of 180°. Adjacent angles are next to, and thus share, one side. A reentrant angle is an inward-pointing angle of a concave polygon. In spherical geometry, a spherical angle is that formed by intersecting
arcs of two great circles; its magnitude
is equal to that of the angle between the two planes of the great circles. See also solid angle. ## ProtractorA protractor is an instrument for measuring angles. Usually semicircular, it is marked off in degrees along the semicircular edge.## Related category• GEOMETRY | ||||||||||

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