How would you set up the midpoint formula if only the midpoint and one coordinate is given? For example, if the midpoint is (2, 5) and the first coordinate is (2, 3)?
Just remember that the x and y distances from any endpoint to the midpoint, must be the same distance from the midpoint to the second endpoint.
The x-distance from the endpoint to the midpoint
The y-distance from the endpoint to the midpoint
Next, add these same distances to the midpoint coordinate to find the other endpoint:
hope that helped