A planet of mass M moves around the Sun along an ellipse so that its minimum distance from the Sun is equal to r and the maximum distance to R. Making use of Kepler's laws, find its period of revolution around the Sun.

Explanation

Semi-major axis `=(r+R)//2`
It is sufficient to consider the motion be along a circle of semi-major axis `(r+R)/(2)` for T does not depend on eccentricity.
Hence `T=(2pi((r+R)/(2))^(3//2))/(sqrt(gammam_s))=pisqrt((r+R)^3//2gammam_s)`
(again `m_s` is the mass of the Sun)