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GFCP - Defining Geometric Terms Lesson

Geometric Terms

Now that we are beginning our unit on Geometry, we need to start out by defining some very important terms and concepts. We are going to study geometrical relationships in the coordinate plane!

TERM	DEFINITION	PICTURE
Point	A location in a plane, named by a letter. A point has no length, width or thickness.	The location of this point is (1, 3) and the name of the point is A.
Line	An infinite set of points with no thickness whose length continues in two opposite directions infinitely. A line named $LaTeX: \overleftrightarrow{AB}$ $\overleftrightarrow{AB}$ indicates the line passes through points A and B.	The black line represents line $LaTeX: \overleftrightarrow{AB}$ $\overleftrightarrow{AB}$
Line Segment	A part of a line, named by the beginning and ending point. A segment, $LaTeX: \overline{AB}$ $\overline{AB}$ indicates the segment begins at point A and ends at point B (or vice versa).	The red line represents the line segment $LaTeX: \overline{AB}$ $\overline{AB}$ , a part of line $LaTeX: \overleftrightarrow{AB}$ $\overleftrightarrow{AB}$
Parallel Lines	Two lines are parallel if they lie in the same plane and do not intersect. When referring to lines in the coordinate plane, we can compare the slope of each line to determine if the lines are parallel. $LaTeX: \overleftrightarrow{AB}\parallel \overleftrightarrow{CD}$ $\overleftrightarrow{AB}\parallel \overleftrightarrow{CD}$ indicates line AB is parallel to line CD.	Lines AB and CD both have slopes of 1/2 so we know they will never intersect and are parallel.
Perpendicular Lines	Two lines are perpendicular if they intersect to form a right angle. When referring to lines in the coordinate plane, we can compare the slope of each line and if the slopes are opposite reciprocals then the lines are perpendicular. $LaTeX: \overleftrightarrow{AB}\perp \overleftrightarrow{CD}$ $\overleftrightarrow{AB}\perp \overleftrightarrow{CD}$ indicates line AB is perpendicular to line CD.	Line AB has a slope of 1/2 while line BC has a slope of -2 so we know they intersect at a 90° angle.
Ray	A part of a line that begins at a point and continues forever in one direction. $LaTeX: \overrightarrow{AB}$ $\overrightarrow{AB}$ indicates a ray that begins at point A and continues in the direction of point B infinitely.	The ray above begins at point A and continues beyond point B.
Angle	A figure created by two distinct rays that share a common endpoint (also known as a vertex).	$LaTeX: \angle ABC\:or\:\angle B\:or\:\angle CBA$ $\angle ABC\:or\:\angle B\:or\:\angle CBA$ all have vertex B.
Circle	The set of all points in a plane equidistant from a given point, for which the circle is named.	All of the points on the circle above are 3 units away from point A. The name of the circle is Circle A.

Defining Geometric Terms Practice

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