Find the other end point
endpoint (5,-1) midpoint (5,10)

The other endpoint would be (5,21).

First find the distance from the endpoint you the mid point. Because the endpoint and midpoint lie on the same x value but different y value you would add the absolute values of the two y values because they are in different quadrants. The distance from the end point and mid point is 11 units.

Because a midpoint halves two endpoints you would just add the distance to itself again to the midpoint. (5, 10+11) which will then give you (5, 21).

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