A certain relation * is defined on the set R^2 by (x1, x2) * (y1, y2) if and only if there exists a real number 0 < k <= 1 such that y2 = kx1 and x2 = ky1. For each of the following questions, be sure to provide a proof supporting your answer.
a) Is * reflexive?
b) Is * symmetric?
c) Is * anti-symmetric?
d) Is * transitive?
e) Is * an equivalence relation, a partial order, both, or neither?