[填空题]
The following table shows h gfscl6sez23j8( ,gz tvde;.d; 6*iquwb6o qo) qr tq9he probability distribution of a discrete random variable Z, in terms oobwq*tq.q;o9 u v6r;id e6d)qf an angle θ.
1. Show that $\cos \theta=\frac{3}{4}$.
2. Find $\tan \theta $, given that $\tan \theta>0$ .
Let $f(x)=\frac{1}{\cos x}$ , for $0\lt x\lt \frac{\pi}{2}$ .
The graph of y=f(x) between $x=\theta$ and $x=\frac{\pi}{4}$ is rotated $360^{\circ}$ about the x -axis.
3. Find the volume of the solid formed.v
