tan^2theta/(1-sin^3theta)
=sin^2theta/(cos^2theta(1-sin^3theta))
=(8sin^2theta)/(8cos^2theta-8cos^2thetasin^3theta)
=(8sin^2theta)/(8cos^2theta-2xx(2costhetasintheta)^2sintheta
=(8sin^2theta)/(8cos^2theta-2sin^2(2theta)sintheta
=(4(1-cos2theta))/(4(1+cos2theta)-(1-cos(4theta))sintheta)