A midpoint is exactly what it sounds like: a midpoint or a central point on a line. The basic midpoint formula is: (x[sub]2[/sub]+x[sub]1[/sub])/2, (y[sub]2[/sub]+y[sub]1[/sub])/2. You can also be given an endpoint and the MIDPOINT, not the other endpoint. If this happens, you take similar steps. You take x value of the endpoint that you do know and add "x". Then, you divide by 2 and set it all equal to the x value of the midpoint. Next, you go on to do the same thing for the y coordinate, but you switch the y values according to the endpoint and midpoint.

So first, find the x coordinates of the two endpoints, in this case, 2 and -1. Take x[sub]2[/sub] and add the x[sub]1[/sub](2+(-1)). Then, divide this by two, and for the x value of the midpoint, you get 0.5! Next, do the same thing for the y coordinates: y[sub]2[/sub]+y[sub]1[/sub] (5+2). Once again, divide this by two, and the y value of the midpoint is 3.5! Finally, put them together, and the midpoint equals (0.5,3.5).