175 The monotonic increasing interval of the function $y=\sqrt{\operatorname{arc} \cos x-(\arccos x)^{2}}$ is $\qquad$
$175\left(-1, \cos \frac{1}{2}\right)$. Let $t=\arccos x$, then $0 \leqslant t \leqslant \pi \cdot t-t^{2}=\frac{1}{4}-\left(\frac{1}{2}-t\right)^{2}$ is decreasing when $t \geqslant \frac{1}{2}$. Therefore, $y=\sqrt{\arccos x-(\arccos x)^{2}}$ is increasing on $\left(-1, \cos \frac{1}{2}\right)$.