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

Free flashcards from Peabody at peabody.kids/flashcards/math-angles-lines