Expert: Steve Holleran - 3/25/2008

Question
Write a function rule for the input-output table.

input  x -3,0,3,6
output y  1,0,-1,-2

Answer
Hi Norma,

When you have these kinds of questions, its easy if you use the idea that the function is linear.  Treat the numbers in the table as points:

 (-3, 1)   (0, 0)    (3, -1)    (6, -2)

Take any two points and find the slope.  Lets take the first two:

  m = change in y / change in x = (1-0) / (-3-0) = - 1/3

Now use point-slope form for a line, taking (0, 0):

                  y - 0 = -1/3 * (x - 0)

and you get        y = -1/3 * x.

Hope this helps you out.

Steve