For two planets 1 and 2 orbiting the same star with orbital periods T1,T2 and orbital radii r1,r2, which of the following relations represents Kepler’s third law?
(a) T22T12=r13r23
(b) T23T13=r22r12
(c) T22T12=r23r13
(d) T2T1=r23r13