6.39. Consider a two-dimensional isotropic harmonic oscillator of mass m represented by x(t) = A cos wt and y(t) B sin wt Show that under the appropriate initial conditions and proper coordinate system, the angular mo- mentum L and total energy E are Vkm AB What is the expression for r in terms of L, E, k,and w? L= = = and E = k(A + B)