(−4, 10)
Step-by-step explanation:
If M is the midpoint of AB, then ...
M = (A + B)/2
2M = A + B . . . . . . multiply by 2
2M -A = B . . . . . . . subtract A
2(-1, 8) -(2, 6) = (-2-2, 16-6) = (-4, 10)
It can be worthwhile to remember how to get the endpoint from the other end and the midpoint: B = 2M - A.