\magnification = \magstep1

$$
P^2 \quad = \quad {{1}\over{M}} \ a^3
$$

$$
M \quad = \quad {{a^3}\over{P^2}}
$$

$$
{{v^2}\over{R}} \quad = \quad a_{\rm cent} \quad = \quad {{G M}\over{R^2}}
$$

$$
M \quad = \quad {{v^2 \thinspace R}\over{G}}
$$



\bye
