Two vertices $\mathrm{A}$ and $\mathrm{B}$ of a triangle $\mathrm{ABC}$ are $(-3,0)$ and $(3,0) .$ The vertex $\mathrm{C}$ is varying in such a way that $4 \tan \frac{\mathrm{A}}{2} \tan \frac{\mathrm{B}}{2}=1$. The locus of $\mathrm{C}$ is
(a) $\frac{x^{2}}{16}+\frac{y^{2}}{25}=1$
(b) $\frac{x^{2}}{25}+\frac{y^{2}}{9}=1$
(c) $\frac{x^{2}}{16}+\frac{y^{2}}{9}=1$
(d) $\frac{x^{2}}{25}+\frac{y^{2}}{16}=1$