Find a if the point (3,a) is on the line that passes through (-2,7) and (5,-3).

Your first step is to find the slope of the line. You can find that using the formula . Plug the x- and y- values from the coordinate pairs into the formula.
 
  Plug in the coordinates
  Cancel out the double negative
  Add and subtract


Next, you can use the same formula to find a by setting it against the slope you just found.

slope =    Plug in the values
=    Subtract
=    Multiply both sides by 7
-10 =   Use the Distributive Property
-10 =   Multiply both sides by -5
50 = 49 - 7a   Subtract 49 from both sides
1 = -7a   Divide both sides by -7
= a   Switch the sides to make it easier to read
a =

This is the graph x=1