Find all critical numbers of the function $f(x) = \sin^2 6x + \cos 6x$,
$0 < x < \frac{\pi}{3}$.
No answer text provided..
$\frac{\pi}{18}, \frac{\pi}{12}, \frac{\pi}{9}, \frac{\pi}{4}$
$\frac{\pi}{18}, \frac{\pi}{6}, \frac{5\pi}{18}$
$\frac{\pi}{36}, \frac{\pi}{6}, \frac{2\pi}{9}$
$\frac{\pi}{24}, \frac{\pi}{6}, \frac{\pi}{2}$
$\frac{\pi}{6}, \frac{5\pi}{24}, \frac{7\pi}{24}$