Random Angle to Co-Function or Supp-Function Identity

Turn an angle lets say $\frac{3\pi }{5}$ into terms of $\frac{\pi }{2}+\theta$ so that would be $\frac{\pi }{2}+\frac{\pi }{10}$ Follow the Co-Function Identities or Supplementary Function Identities method depending on what multiple of pi you clamped to.