The point at which two lines intersect has opening {angle, geometry} between lines.
Lines {bisector, angle}| can divide angles in half.
Angles have sides {half-line} {ray, angle}.
Bisectors {internal bisector} can be perpendicular to external bisector.
In tessellations, vertexes {nodal point, tessellation} can be common to three or more polygons.
Circles can divide into 360 equal arcs {degree, angle}. Degrees can divide into 60 parts {minute, angle}. Minutes can divide into 60 parts {second, angle}.
Angle units {grad} {grade, angle} can equal 1/100 right angle.
2*pi radians, or 360 degrees, make one revolution {perigon}.
Circles with one-unit-length radius have circumference 2*pi radians, so 360 degrees equals 2*pi radians {radian, angle}. One radian equals 360 / (2 * pi) degrees or 57 degrees.
Angles {acute angle}| can be less than 90 degrees.
Two angles {complementary angle}| can add to 90 degrees.
Two angles {corresponding angle, plane} can have parallel corresponding sides.
One ray {initial side} can be stationary and one ray {terminal side} can rotate, so angle {directed angle} changes.
Two angles {equal angle} with parallel sides are equal.
Polygon sides make angles {exterior angle} outside polygon vertices. External angle is 360 degrees minus internal angle.
Two polygon sides make an angle {interior angle} {internal angle} inside a polygon vertex.
Angles {obtuse angle}| can be between 90 and 180 degrees.
Angles {quadrantal angle} can be (n * pi) / 2 radians, where n = 0, 1, 2, ..., for 0, 90, 180, ... degrees.
Angles {reflex angle, size} can be greater than pi radians and less than two times pi radians.
Angles {straight angle} can be pi radians.
Two angles {supplementary angle}| can add to 180 degrees.
Two lines intersect to form opposite angles {vertical angle}.
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Date Modified: 2022.0225