Graph it and see that it looks like a straight line. Assume, for the moment, that it is a linear function. Use the two-point form of the equation of a straight line to derive an equation using any two of the three given points.
where and are the coordinates of the two points you chose from the given three points.
Do the indicated arithmetic.
Substitute the coordinates of the point you did not use to derive the equation into the equation in place of and . Do the arithmetic to verify that the third point is in fact an element of the solution set of the derived equation.
