Homework Statement
Hi all.
A particle can choose randomly to move in one of these directions:
r_1 = (a,0), \quad r_2 = (-a,0), \quad r_3 = (0,a) \quad \text{and}\quad r_4 = (0,-a).
These are vectors, not coordinates! I have to find the mean of the square of r, i.e. <r> after n...