| A | B |
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| point | An undefined term in geometry. A point can be thought of as a dot that represents a location on a plane or in space. Geometric points have no size. |
| line | An undefined term in geometry. A line is perfectly straight, contains an infinite number of points, extends infinitely in 2 directions and has no thickness. |
| plane | An undefined term in geometry. A plane is a flat surface that extends infinitely in all directions. |
| collinear | lying in the same line (any 2 points are collinear) |
| coplaner | lying on the same plane (Any 3 points are coplaner |
| segment | a part of a line that begins at one point and ends at another |
| ray | a part of a line that starts at a point and extends infinitely in one direction |
| endpoint | a point at an end of a segment or the starting point of a ray |
| angle | a figure formed by 2 rays with a common endpoint |
| vertex of an angle | the point in common of the two rays that form an angle |
| sides of an angle | the 2 rays that form an angle |
| interior of an angle | The area between the rays that make up an angle |
| intersection | geometric figures that have one or more points in common |
| postulates | a statement that is accepted as true without proof (a fundamental geometry idea) aka: axioms |
| length of a segment | the measure of the distance from one endpoint to the other |
| congruent | figures that have the same size and same shape. Congruent segments are segments that match exactly |
| tick marks | show which segments are known to be congruent |
| complementary angles | two angles whose measures have a sum of 90 degrees. Each angle is called the complement of the other. |
| supplementary angles | two angles whose measures have a sum of 180 degrees. Each angle is called the supplement of the other. |
| linear pair | when the endpoint of a ray falls on a line so that two angles are formed. 2 angles that are linear pair are supplementary |
| right angle | an angle whose measure is 90 degrees |
| acute angle | an angle whose measure is less than 90 degrees |
| obtuse angle | an angle whose measure is more than 90 degrees and less than 180 degrees |
| straight angle | an angle whose measure is 180 degrees |
| perpendicular lines | two lines that intersect to form a right angle |
| parallel lines | two coplaner lines that do not intersect |
| segment bisector | a line that divides a segment into two congruent parts. A bisector that is perpendicular to a segment is called a perpendicular bisector |
| midpoint | a point where a bisector intersects a segment |
| angle bisector | a line or ray that divides an angle into 2 congruent angles |
| angle arcs | like tick marks- show which angles are known to be congruent |
