Answer:
If the bisector of AB is at origin (0,0) and A is at (4,0)
we can say that the mid-point of the line AB is at (0,0)
Hence, the point B will be 4 units on the other side of the origin
Therefore, the co-ordinates of B are: (-4,0)
Since the line AB is 4 units to the left and 4 units to the right of the origin,
the length of line-segment AB is 4 + 4 = 8 units