Undefined term
AB  
A basic figure that is not defined in terms of other figures.
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Collinear  Points that lie on the same line. 
Plane  A flat surface that has no thickness and extends forever. 
Line  A straight path that has no thickness and extends forever. 
Point  A location that has no size. 
Coplanar  Points that lie in the same plane. 
Endpoint  A point at an end of a segment or the starting point of a ray. 
Ray  A part of a line that starts at an endpoint and extends forever in one direction. 
Postulate  A statement that is accepted as true without proof, also called an axiom. 
Vertex  The common endpoint of the sides of an angle. 
Opposite rays  Two rays that have a common endpoint and form a line. 
Segment  A part of a line consisting of two endpoints and all points between them. 
Distance  The absolute value of the difference of the coordinates of two points. 
Construction  A method of creating a figure that is considered to be mathematically precise. 
Between  Given three points A, B, and C, B is between A and C if and only if all three of the points lie on the same line, and AB + BC = AC. 
Coordinate plane  A plane that is divided into four regions by a horizontal line called the xaxis and a vertical line called the yaxis. 
Coordinate  A number used to identify the location of a point. 
Congruent segments  Two segments that have the same length. 
Degree  A unit of angle measure. 
Midpoint  The point that divides a segment into two congruent segments. 
Bisect  To divide into two congruent parts. 
Angle  A figure formed by two rays with a common endpoint. 
Measure  The use of units to find a size or quantity. 
Segment bisector  A line, ray, or segment that divides a segment into two congruent segments. 
Vertical angles  The nonadjacent angles formed by two intersecting lines. 
Straight angle  An angle formed by two opposite rays that measures 180°. 
Acute angle  An angle that measures greater than 0° and less than 90°.
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Right angle  An angle that measures 90°. 
Interior of an angle  The set of all points between the sides of an angle. 
Obtuse angle  An angle that measures greater than 90° and less than 180°. 
Exterior of an angle  The set of all points outside an angle. 
Adjacent angles  Two angles in the same plane with a common vertex and a common side, but no common interior points. 
Complementary angles  Two angles whose measures have a sum of 90°. 
Supplementary angles  Two angles whose measures have a sum of 180°. 
Angle bisector  A ray that divides an angle into two congruent angles. 
Linear pair  A pair of adjacent angles whose noncommon sides are opposite rays. 
Congruent angles  Angles that have the same measure. 
Image  A shape that results from a transformation of a figure. 
Preimage  The original figure in a transformation. 
Reflection  A transformation across a line. 
Transformation  A change in the position, size, or shape of a figure. 
Rotation  A transformation about a point P, such that each point and its image are the same distance from P. 
Translation  A transformation in which all the points of a figure move the same distance in the same direction. 
leg  One of the two sides of the right triangle that form the right angle. 
Area  The number of nonoverlapping unit squares of a given size that will exactly cover the interior of a plane figure. 
Hypotenuse  The side opposite the right angle in a right triangle. 
Length  The distance between the two endpoints of a segment. 
base  Any side of a triangle. 
Height  Asegment from a vertex that forms a right angle with a line containing the base. 
Radius  A segment whose endpoints are the center of a circle and a point on the circle, or the distance from the center of a circle to any point on the circle. 
Perimeter  The sum of the side lengths of a closed plane figure. 
pi  The ratio of the circumference of a circle to its diameter, denoted by the Greek letter π. 
Circumference  The distance around the circle. 
Diameter  A segment that passes through the center of a circle and whose endpoints are on the circle, or the length of such a segment. 

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