I cant see the image...but I take it that the midpoint is (9,8) and the endpoint S is (10,10) and ur looking for the other endpoint R.
midpoint formula : (x1 + x2) / 2, (y1 + y2) / 2
(10,10)....x1 = 10 and y1 = 10
(x,y)....x2 = x and y2 = y
so we sub
(10 + x) / 2, (10 + y) / 2 = 9/8
(10 + x) / 2 = 9
10 + x = 9 * 2
10 + x = 18
x = 18 - 10
x = 8
(10 + y) / 2 = 8
10 + y = 8 * 2
10 + y = 16
y = 16 - 10
y = 6
so endpoint R has coordinates of (8,6) <===
