\[\frac{(\operatorname{dn}z_{2}+\operatorname{dn}z_{3})(\operatorname{dn}z_{3}+%
\operatorname{dn}z_{1})(\operatorname{dn}z_{1}+\operatorname{dn}z_{2})}{%
\operatorname{dn}z_{1}+\operatorname{dn}z_{2}+\operatorname{dn}z_{3}}\]