Acute angle: One less than 90 degrees
Adjacent angle: Either of two angles having a common side and a common vertex
Angle: A shape, formed by two lines or rays diverging from a common point (the vertex)
Angle bisector: A line segment that bisects one of the vertex angles of a triangle
Area: A particular geographical region of indefinite boundary
Between-ness: The quality or state of being between two others in an ordered mathematical set
Bisect: To divide into two usually equal parts
Complementary Angles: Two angles added together equaling 90 degrees
Congruent angles: Two angles are congruent angles if and only if they have the same measure
Congruent segments: Two segments are congruent segments if and only if they have the same measure
Collinear: Collinear points lie along a straight line
Coplanar: Coplanar objects are those lying in the same plane
Endpoint: The physical change which results when the equivalence point has been reached
Exterior: (Outside) The region that is outside of something
Interior: An angle facing the interior or inside of a polygon or shape
Line: One dimensional object; extends forever
Linear pair: A pair of adjacent angles whose non-common sides are opposite rays
Line Segment: A part of a line that is bounded by two distinct end points
Midpoint: A position midway between two extremes
Non-collinear: Points not lying on the same line
Non-coplanar: Points not lying on the same plane
Obtuse angle: An angle whose measure is in between 90 and 180 degrees
Opposite Rays: Two rays with a common endpoint that form a straight line
Perimeter: The boundary of a system or network, which defines the inside and outside
Perpendicular lines: At right angles. A line is perpendicular to another if they meet at 90 degrees
Plane: Set of points making up a flat two-dimensional surface that has length and width but no depth
Point: A precise location or place on a plane
Rotation: The act or process of turning around a center or an axis
Ray: Extends forever in one direction
Right angle: An angle formed by the perpendicular intersection of two straight lines; an angle of 90
degrees
Straight angle: An angle whose measure is greater than 0 but less than 90 degrees
Supplementary angle: Two angles that add up to 180 degrees
Triangle: The plane figure formed by connecting three points not in a straight line by straight line
segments; a three-sided polygon.
Vertex: Common endpoint on two rays
Vertical Angles: Either of two equal and opposite angles formed by the intersection of two straight lines
Alternate exterior angles: When two lines are crossed by another line, the pairs of angles on opposite
sides of the transversal but outside the two line are called Alternate Exterior Angles
Alternate interior angles: When two lines are crossed by another line, the pairs of angles on opposite
sides of the transversal but inside the two lines are called Alternate Interior Angles
Consecutive interior angle: When two lines are crossed by another line, the pairs of angles on one side
of the transversal but inside the two lines are called Consecutive Interior Angles
Corresponding angle: Two nonadjacent angles made by the crossing of two lines by a third line, one
angle being interior, the other exterior, and both being on the same side of the third line
Parallel lines: Lines that are always the same distance apart and will never meet
Skew lines: Straight lines that are not in the same plane and do not intersect
Parallel planes: They lie on a same plane and they cannot intersect because they lie on parallel planes
Transversal: A line that cuts across two or more lines
Slope: To diverge from the vertical or horizontal
Acute triangle: Triangle whose interior angles are all acute
Base Angles: Either of the two angles of a triangle that have the base for a side
Congruent Triangles: Are triangles that are the same size and the same shape
Equilateral Triangle: A three sided regular polygon
Equiangular Triangle: A triangle whose angles are all equal
Included Angle: Made by two lines with a common vertex
Included Side: Angle made by two lines with a common vertex
Isosceles Triangle: A triangle with two equal sides
Altitude: The height of a thing above a reference level, especially above sea level or above the earth's
surface
Hypotenuse: The side of a right triangle opposite the right angle
Median: Relating to, located in, or extending toward the middle
Circumference: The circle that contains the three vertices
Vertex angle: A triangle with two equal sides
Obtuse angle: A triangle that contains an obtuse interior angle
Reflection: The act of reflecting or the state of being reflected.
Right Triangle: A triangle with one right angle
Scalene Triangle: A triangle with no two sides of equal length
Translation: The original object and its translation have the same shape and size, and they face in the
same direction
Concurrent: Happening at the same time as something else. Operating or acting in conjunction with
another. Concurrent meeting or tending to meet at the same point; convergent
Perpendicular bisector: A line which cuts another line into two equal parts at 90 degrees
Centroid: A system of masses each of whose coordinates is a wighted mean of coordinates of the same
dimension of points within the system, the weights being determined by the density function of the
system
Incenter: It is the meeting point of the three angle bisectors