To Write the Equation of a Line:
I. 1. Slope
(m) : You must
be given or be able to find
the slope.
2. y-intercept
(b) : You must
be given or be able to
find the y-intercept.
3. Then
use the slope-intercept form of the equation of
the line:
y = mx + b
II. 1. Slope
(m) : You must
be given or be able to find
the slope.
2. Point 
: You must be given a
point.
3. Then
use the point-slope form of the equation
of the line:
Parallel
Lines have the same slopes: 
Perpendicular
Lines have slopes that are negative reciprocals: 
Slope
(average rate of change): 
y = b : Constant Function (horizontal line)
x = a : Not
a function (vertical line)
: Standard Form of the Equation of a Line.