For the curve $\;y=3 sin \theta cos \theta \;,x=e^{\theta} sin \theta\;, 0 \leq \theta \leq \pi ,\;$ the tangent is parallel to x - axis when $\;\theta\;$ is :

Question

$(a)\;\large\frac{3\pi}{4} \qquad(b)\;\large\frac{\pi}{2}\qquad(c)\;\large\frac{\pi}{4}\qquad(d)\;\large\frac{\pi}{6}$