* Compute the area of triangle formed by three points using [Heron's * formula](https://en.wikipedia.org/wiki/Heron%27s_formula). * If the lengths of the sides of the triangle are \f$a,\,b,\,c\f$ and * \f$s=\displaystyle\frac{a+b+c}{2}\f$ is the semi-perimeter then the area is * given by \f[A=\sqrt{s(s-a)(s-b)(s-c)}\f] * \param [in] A vertex A * \param [in] B vertex B * \param [in] C vertex
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