$\sin\large\frac{9\pi}{14}$$\sin\large\frac{11\pi}{14}$$\sin\large\frac{13\pi}{14}$ is equal to

Question

$(a)\;\large\frac{1}{64}$$\qquad(b)\;\large\frac{-1}{64}$$\qquad(c)\;\large\frac{1}{8}\qquad$$(d)\;\large\frac{-1}{8}$