Show that Keplar's third law works for each of the terrestrial planets?

Answer 1

It works for all planets. Look up the Period, P, and the (average) Radial distance from the sun, R, for the terrestrial planets Mercury, Venus, Earth and Mars.

The average radial distance is also called the semimajor axis.

Prove to yourself that P^2/R^3 is the same constant for all of those planets