Start with the midpoint, G(10,8), and move your pencil point 4 units to the left and 1 unit up to reach the endpoint M(6,9). To find the other end point, start with the midpoint G(10,8) again, but now move your pencil point 4 units to the right and 1 unit down. Result: N(14,7).
Check: find the mean of the 2 x-coordinates: Does (6+14)/2 = 10, the x-coordinate of the midpoint? YES. Does (9+7)/2 = 8, the y-coord. of the midpoint? YES.
The desired other end point is therefore N(14,7).
