Use the slope, m, defined below to test for linearity of functions:

General Formula: y = b + m x (main form used in class)

The slope or rate of change of y with respect to x: 
            and b is the y - intercept, i.e. The value of y when x = 0.

The slope, m, is negative when the function is decreasing: Depreciation or Decay
            (i.e. as x gets large, y gets small)

Slope-point form:

        y - y₀ = m (x - x₀)
 

General form of Linear Formula:

      Ax + By + C = 0 , where A, B, and C are constants
 

Intersections of Linear Functions:

  I. parallel lines have same slopes, so m1 = m2
        ( if m1 is slope for line 1 and m2 is slope for line 2)
 

  II. perpendicular lines have inverse slopes, so m1 =
        (if line 1 is perpendicular to line 2)
 

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