1. The problem statement, all variables and given/known data Prove that: r=a(cos E-e)(ihat,xi)+(sqrt(a*p)) *sin E (ihat,eta) 2. Relevant equations E=eccentric anomaly e=eccentricity 3. The attempt at a solution Rotational matrices come into play here, but I'm not sure to what extent. alpha=beta*gamma*delta, with their respective matrices. This appears to have no 3rd component on it (only xi and eta). I have all of the equations for E, e, p, a, theta, and so on to substitute in for the proof. How is the rotational matrix involved?