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# Points and Lines

Point
A point indicates a position.
Two points determine a line.
Line
A line is a straight line that extend in either direction.
Plane
A plain is a set of points that forms a flat surface. Three noncollinear points determine a plane. For example, A,B,C are three noncollinear points.
Line Segment
A line segment is a part of a line consisting of two points, called end points, and the set of all points between them. For example, AB is a line segment.
Ray
A ray is a part of a line consisting of a given point, called the end point, and continues forver in one direction.
Angle
An angle is the union of two rays having the same end point. The end point is called the vertex of the angle, the rays are called the sides of the angle. For example, angle BAC or angle CAB or angle A.
Collinear points
Collinear points are points which lie on the same line. For example, A,B,C are collinear points.
Parallel Lines
Parallel lines are never intersect. For example, line m and line n are never intersect.
Acute Angle
An acute angles is any angle whose measure is less than 90 degrees. For example, angle b is a acute angle.
Right Angle
A right angle has a measure of 90 degrees. For example, the angle ACB is 90 degrees.
Obtuse Angle
Obtuse angle is an angle whose measure is more than 90 degrees but less than 180 degrees. For example, angle1 is an obtuse angle. The measure of angle1 is more than 90 degrees and less than 180 degrees.
Straight Angle
An Angle with a measure of 180 degrees is a straight angle. For example, angle ABC or angle CBA has a measure of 180 degrees. It is a straight angle. Note: the vertex of the angle and its two sides lie on the same line.
Betweeness For Points
Point X is between point A and B if (1). Points A, X, and B are collinear and (2). AB = AX + XB , for example, point X is between point A and point B.
Betweeness For Ray
If ray BX lies in the interior of angle ABC, then angle ABC = angle ABX + angle XBC.
Congruent Line Segments
Lines segments are said to be congruent if they have the same measure. For example, AB=10ft, CD=10ft, then AB=CD.
Congruent Angles
Angles are said to be congruent if they have the same measure. For example, angle ABC = 90 degree, angle DEF = 90 degree, then angle ABC = angle DEF.
MidPoint
Point X is the midpoint of AB if (1). X is between A and B and (2). AX = XB. For example, since AX=5 ft, XB=5 ft, then AX=XB. ie, X is the midpoint of line segment AB.
Angle Bisector
OX is the bisector of angle AOB if (1). X lies in the interior of angle AOB and (2). angle AOX is congruent to angle XOB. For example, OX is the bisector of angle AOB.
Bisector Of A Line Segment
A bisector of a line segment AB is any line, ray or segment which passes through the midpoint of AB. For example, the blue line is the bisector of line segment AB.