This is a free lesson from our course in Geometry

In this lesson you’ll learn the concepts of Ray, Line Segment, Parallel and Perpendicular lines & their important properties/usages in Geometry. It is described in the presentation by instructor using video and with the help of several examples with solution.
A ray is a part of line that consists of a point on the line called an endpoint and all other points on one side of the endpoint. It is represented by: A line segment is a ‘straight’ line that you might draw using the ruler on a piece of paper. A line segment does not extend infinitely, but has two designated endpoints. The terms ‘segment’ and ‘straight line segment’ are also used to refer a line segment. Its length is a measure of its size and is the same as the distance between its endpoints. (More text below video...)
Other useful lessons:
 Point, Line, and Plane Midpoint and Congruence Classifying Angles
(Continued from above)  The line segment AB is represented as . There are no arrow heads on the line over AB as in case of a line or ray. E.g. the following is a diagram of line segment AB:
Two or more lines are called parallel lines if and only if the lines lie in the same plane but do not intersect. Also they have same slope. All vertical lines are parallel. When two lines are parallel, they have no points in common. The symbol used for parallel lines to each other is . E.g. Line AB is parallel to CD is represented by AB CD, as shown below:
Perpendicular lines are lines that intersect to form a right or 90 degree angle. If two lines are perpendicular to each other, then the product of their slopes is equal to – 1.The figure below shows, the lines AB and CD are perpendicular to each other.
Further on you’ll learn to find if the lines are parallel or perpendicular in the given case and their properties. For example: to find the number of points of intersection for one pair of perpendicular lines, you may follow the steps given below:
• two lines are perpendicular intersect at right angles.
• any two perpendicular Lines intersect at exactly one point, is the final answer.

Remember:
• In a plane; if a line is perpendicular to one of two parallel lines, it is perpendicular to the other line as well
• in a plane; if a line is parallel to one of two parallel lines, it is parallel to both parallel lines.
• in a plane; if three or more parallel lines are intersected by two or more transversals, then they divide the transversals proportionally.
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