The Y coordinates are the same for the given end point and the midpoint, so it would also be -2 for the other end point.
The distance from the given end point to the midpoint for the x value is from 1 to -4, which would be 5 units. To find the other end point move 5 units away from the midpoint: -4 - 5 = -9
The other endpoint would be (-9,-2)