If you have a table, you will have x- and y-values: (x, y).
Calculate the slope of the line connecting any two points. Then repeat this. If you get the same slope each time, then you may conclude that the function is linear.
Also: If you have y = mx + b with m and b known, subst. each of the given x-values and calculate y in each case. Do the calculated y-values agree with the given y-values? If so, the function is linear and the graph is a str. line.
