Hey, im a bit stuck with this question, not sure where to start:

The iterative sequence x1,x2,x3...., where xr+1 = g(x), has a fixed point a, so that a=g(a). Given that xr+1 - a implies k(xr - a), show that:
k implies (x2 - x1) / (x1-x0)

Any help would be much appreciated