Vertical and Horizontal Lines
The vertical line 
is drawn in blue. Notice that the x coordinate of all the points on the blue line is 5.
The horizontal line 
is drawn in green. Notice that the y coordinate of all the points on the green line is 3.
Parallel Lines
Parallel lines have the same slope.
Move the slider ‘b’ to see a set of lines that all have the same slope.
Perpendicular Lines
Suppose we sit a box that measures 5 by 3 on the x axis as shown below. The diagonal line drawn has slope -5/3.
Rotate the box to see that when a line is rotated a full 90 degrees, the rise and run are interchanged, and a negative slope becomes a positive slope.
In general, if slope of line 1 is
![\[\frac{a}{b}\]](https://tentotwelvemath.com/wp-content/ql-cache/quicklatex.com-42aa3ac0f90fb4110ea56aaccff9e797_l3.png "Rendered by QuickLaTeX.com")
and if slope of line 2 is
![\[-\frac{b}{a}\]](https://tentotwelvemath.com/wp-content/ql-cache/quicklatex.com-09f88b3ea4465434b049ed138b7bb845_l3.png "Rendered by QuickLaTeX.com")
then lines 1 and 2 are perpendicular to each other.