Jan G. answered • 03/26/19

Mechanical engineer with several years of tutoring experience

Here's a suggestion:

Determine the equation of the straight line that goes through points 1 & 2. Standard form: y = mx + b.

Next, substitute x_{3} into this equation to get the y coordinate of the point on this line for x = x_{3. }

Let's call this point 4, with coordinates (x_{3},y_{4}).

Calculate the vertical distance between point 3 and point 4:

If y_{3} - y_{4} > 0, then point 3 lies above the line (to the "left").

If y_{3} - y_{4} < 0, then point 3 lies below the line (to the "right").

Hope that helps.