Question 784700
Let (p,q) be the other unknown endpoint


According to the midpoint formula, if we have two endpoints (x1,y1) and (x2,y2), the midpoint MP is MP = (Mx, My)


where


Mx = (x1 + x2)/2


My = (y1 + y2)/2



So this means that


X coordinate of the midpoint


Mx = (x1 + x2)/2


1 = (-9 + p)/2


1*2 = -9 + p


2 = -9 + p


2 + 9 = p


11 = p


p = 11


So the x coordinate of that unknown endpoint is 11


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Y coordinate of the midpoint


My = (y1 + y2)/2


5 = (5 + q)/2


5*2 = 5 + q


10 = 5 + q


10 - 5 = q


5 = q


q = 5


and the y coordinate of that unknown endpoint is 5


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Since p = 11 and q = 5, the point (p,q) turns into (11,5)



The final answer is <font color="red">(11,5)</font>