Call the midpoint M. Then it must satisfy
... M = (R + S)/2
... 2M = R + S . . . . multiply the above equation by 2
... R = 2M -S . . . . . subtract S
Since we need to use this equation several times, it is convenient to calculate ...
... 2M = 2(6, -10) = (12, -20)
All we need to do is subtract the given value of S from this.
10. R = (12 -0, -20 -8) = (12, -28)
11. R = (12 -9, -20 -(-3)) = (3, -17)
12. R = (12 -(-2), -20 -(-7)) = (14, -13)
