Question 21Consider a pyramid $P\text{-}ABCD$ whose base $ABCD$ is square and whose vertex $P$ is equidistant from $A,$ $B,$ $C,$ and $D.$ If $AB=1$ and $\angle APB=2\theta,$ then the volume of the pyramid is$\frac{\sin\theta}{6}$$\frac{\cot\theta}{6}$$\frac1{6\sin\theta}$$\frac{1-\sin2\theta}{6}$$\frac{\sqrt{\cos2\theta}}{6\sin\theta}$