
For
any two lines in the same plane, one of two relationships can
occur: the lines will run parallel to each other, or they will
intersect. 

Lines m
and l
are parallel lines. They will travel to infinity in either direction
and never intersect. 
Lines x
and y
are intersecting lines. Lines can only intersect at one point
and only one point. 


When two lines intersect
and form right angles, they are called perpendicular lines.
Lines s and t
are perpendicular lines.
Vertical
Angles 
When two parallel
lines are cut by another line (a transversal) angles
of equal measure are created.
The measures of L2 =L3,
the measure of L1=L4.
Angles 2 and 3 are called
alternate interior angles.
Angles 1 and 4 are called
alternate exterior angles.


Practice
