equation icon  tanYn = ---rS-sin-(k(fS-+-2np))---, (146) rS cos(k(fS + 2np)) - r0 V~ r2-+-r2---2r-r--cos-(k(f---+-2np)) tanQn = ---S----0-----S--0--------S---------, (147) V~ ---------------zS--------------------- 2 2 2 sn = zS + rS + r0- 2rSr0 cos(k(fS + 2np)). (148)