Find the maxima and minima of the magnitude

[imy786]

Homework Statement

A hypothetical star S has a planet P that moves in an elliptical orbit with period T . The minimum distance of P from S is d and the maximum distance is 1.7d.
(i) find the maxima and minima of the magnitude of the acceleration of P, in terms of d and T .

Homework Equations

dont know

The Attempt at a Solution

can anyone give me the equation for this

 

[SGT]

Try Newton´s law of gravitation or Kepler´s laws.

 

[imy786]

a= (2*pi)^2 * ( r^3 / T^2) * 1/ X^2

minimum distance is d
max distance is 1.7 d

do i substitue d for r?