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Acute angle	Between 0° and 90°		math-angles-lines
Right angle	Exactly 90°		math-angles-lines
Obtuse angle	Between 90° and 180°		math-angles-lines
Straight angle	Exactly 180°		math-angles-lines
Reflex angle	Between 180° and 360°		math-angles-lines
Full rotation	360°		math-angles-lines
Complementary angles	Add up to 90°		math-angles-lines
Supplementary angles	Add up to 180°		math-angles-lines
Complement of 30°	60°		math-angles-lines
Supplement of 110°	70°		math-angles-lines
Vertical angles	Opposite angles made by two crossing lines; they are equal		math-angles-lines
Adjacent angles	Share a vertex and a side, with no overlap		math-angles-lines
Linear pair	Two adjacent angles that form a straight line; add up to 180°		math-angles-lines
Corresponding angles	Angles in matching positions at two different crossings of a transversal		math-angles-lines
Alternate interior angles	Angles inside the two lines on opposite sides of the transversal		math-angles-lines
Alternate exterior angles	Angles outside the two lines on opposite sides of the transversal		math-angles-lines
Same-side interior angles	Angles inside the two lines on the same side of the transversal		math-angles-lines
Vertex of an angle	The point where the two rays meet		math-angles-lines
Angle bisector	A ray that splits an angle into two equal angles		math-angles-lines
Protractor	A tool for measuring angles in degrees		math-angles-lines
Line	A straight path that goes on forever in both directions		math-angles-lines
Line segment	A piece of a line between two endpoints		math-angles-lines
Ray	A part of a line with one endpoint, going on forever one way		math-angles-lines
Collinear points	Points that lie on the same line		math-angles-lines
Coplanar	Lying in the same flat plane		math-angles-lines
Parallel lines	Lines in a plane that never meet		math-angles-lines
Perpendicular lines	Lines that meet at 90°		math-angles-lines
Skew lines	Lines in 3D that do not meet and are not parallel		math-angles-lines
Midpoint	The point exactly halfway along a segment		math-angles-lines
Perpendicular bisector	A line that cuts a segment in half at a right angle		math-angles-lines
Transversal	A line that crosses two or more lines		math-angles-lines
Plane	A flat surface that extends forever in every direction		math-angles-lines
Center of a circle	The point equally far from every point on the circle		math-angles-lines
Radius	A segment from the center to the circle		math-angles-lines
Diameter	A chord through the center; the longest chord		math-angles-lines
Chord	A segment joining two points on a circle		math-angles-lines
Secant	A line that cuts through a circle at two points		math-angles-lines
Tangent	A line that touches a circle at one point		math-angles-lines
Arc	A piece of the circle's outline		math-angles-lines
Minor arc	An arc smaller than a semicircle		math-angles-lines
Major arc	An arc larger than a semicircle		math-angles-lines
Semicircle	Half a circle; an arc of 180°		math-angles-lines
Sector	A region bounded by two radii and an arc		math-angles-lines
Segment of a circle	A region bounded by a chord and an arc		math-angles-lines
Central angle	An angle with its vertex at the center of a circle		math-angles-lines
Inscribed angle	An angle with its vertex on the circle		math-angles-lines
Concentric circles	Circles that share the same center		math-angles-lines
Congruent circles	Circles with equal radii		math-angles-lines
Degrees in a circle	360		math-angles-lines
Radians in a full circle	2π		math-angles-lines
Degrees in one radian	About 57.3°		math-angles-lines
Convert 180° to radians	π radians		math-angles-lines
Convert 90° to radians	π/2		math-angles-lines
Convert 60° to radians	π/3		math-angles-lines
Convert π/4 to degrees	45°		math-angles-lines
Convert π/6 to degrees	30°		math-angles-lines