Editing Slope (section)

===Examples===
For example, consider a line running through points (2,8) and (3,20). This line has a slope, {{math|''m''}}, of 
: <math>\frac {(20 - 8)}{(3 - 2)} = 12. </math>

One can then write the line's equation, in point-slope form:
: <math>y - 8 = 12(x - 2) = 12x - 24. </math>
or: 
: <math>y = 12x - 16. </math>

The angle θ between −90° and 90° that this line makes with the {{math|''x''}}-axis is 
:<math>\theta = \arctan(12) \approx 85.2^{\circ} .</math>

Consider the two lines: {{math|1=''y'' = −3''x'' + 1}} and {{math|1=''y'' = −3''x'' − 2}}. Both lines have slope {{math|1=''m'' = −3}}. They are not the same line. So they are parallel lines.

Consider the two lines  {{math|1=''y'' = −3''x'' + 1}} and {{math|1=''y'' = {{sfrac|''x''|3}} − 2}}. The slope of the first line is {{math|1=''m''<sub>1</sub> = −3}}. The slope of the second line is {{math|1=''m''<sub>2</sub> = {{sfrac|1|3}}}}. The product of these two slopes is −1. So these two lines are perpendicular.