S=\frac{1}{\sqrt{\left(\frac{1}{{h}_{a}} +\frac{1}{{h}_{b}}+\frac{1}{{h}_{c}}\right)
\left(\frac{1}{{h}_{a}} +\frac{1}{{h}_{b}}-\frac{1}{{h}_{c}}\right)
\left(\frac{1}{{h}_{b}} +\frac{1}{{h}_{c}}-\frac{1}{{h}_{a}}\right)
\left(\frac{1}{{h}_{a}} +\frac{1}{{h}_{c}}-\frac{1}{{h}_{b}}\right)

}}