Lesson Introduction on Parallel straight lines

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This lesson will deal with concept of parallel lines and investigate into its properties.

<b>Parallel Lines</b>

{{{drawing( 160, 160, -6, 6, -6, 6,line( -3, -3, 3, -3),line( -3,3,3,3),locate(-3.9,-3,C),locate(3.5,3.5,B),locate(3.5,-3,D),locate(-3.9,3.5,A))}}}

Two straight <A HREF=line-ray-and-segments.lesson>lines</A> AB and CD are called parallel straight lines, if they lie in the same plane and don�t intersect however long they may be continued.The parallel lines are denoted as AB|| CD.

<b> Features and properties of parallel lines:</b>

1.> The parallel lines intersect each other at infinity.

2.>For two parallel lines all points of one line are equidistant from another line.

3.>All straight lines which are parallel to one straight line will be parallel to all the lines to which first line is parallel.

4.>It�s adopted that an <A HREF=Introduction-and-Properties-of-Angles.lesson>angle</A> between parallel straight lines is equal to zero. An angle between two parallel <A HREF=line-ray-and-segments.lesson>rays</A> is equal to zero, if their directions are the same, and 180 deg, if the directions are opposite.

{{{drawing( 160, 160, -6, 6, -6, 6,line( -5, 0, 5, 0 ),line( -4,0, -4,4 ), line(0,0, 0,4),line(4,0, 4,4),locate(-5.8,0.5,K),locate(5.5,0.5,M),locate(-4.5,0,B),locate(-4.5,5,A),locate(0,0,D),locate(0,5,C),locate(4,0,F),locate(4,5,E))}}}

5.>If perpendiculars (AB, CD, EF) as shown in figure are drawn to a straight line KM then they are all parallel between themselves.

6.>Inversely, if the straight line KM is perpendicular to one of the parallel straight lines (AB, CD, EF), will be perpendicular to all others.

7.>A length of perpendicular segment, concluded between two parallel straight lines, is a distance between them.

8.>If a line and a plane do not intersect each other then the line will be parallel to plane.

More on concept of <A HREF=http://www.algebra.com/algebra/homework/Points-lines-and-rays/Geometry-Parallel-Lines-and-Transversals.lesson>Transversals and parallel lines.</A>