+6 
been stuck on this question for a while, help much appreciated :) thank you
+845 Right so this is my attempt at the question:
From the graph we know that from B A = -b+a and O A = a
we know that OX = 2a-b, assuming A is in the way if we subtract the value it takes to get to A from O then we get AX= a-b
as 2a-b - a = a-b.
then we can get the value of BX by adding the "distance" of BA and AX which is 2a-2b.
we know that B, A , X lies on the same staight line because AX (a-b) is a factor of BX (2a-2b).
let me know if im wrong 
