$$x = \sin ^ { 2 } \theta + \cos ^ { 4 } \theta , \theta , 5$$
$x=\frac{\cos(4\theta )+7}{8}$
$\theta =\frac{\arccos(7-8x)+2\pi n_{1}-\pi }{4}\text{, }n_{1}\in \mathrm{Z}$
$\theta =\frac{-\arccos(7-8x)+2\pi n_{2}+\pi }{4}\text{, }n_{2}\in \mathrm{Z}\text{, }x\geq \frac{3}{4}\text{ and }x\leq 1$
