sin 2n/5 * cos 7n/30 - sin 7n/30 * cos 2n/5=sin2n*cos7n/150 - sin7n sin2n/150=sin2ncos7n-sin7n-sin2n/150.
sin 2n/5 * cos 7n/30 - sin 7n/30 * cos 2n/5=sin2n*cos7n/150 - sin7n sin2n/150=sin2ncos7n-sin7n-sin2n/150.