9. The solution to the inequality $(\lg 20)^{2 \cos x}>1, x \in(0, \pi)$ is

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9. The solution to the inequality $(\lg 20)^{2 \cos x}>1, x \in(0, \pi)$ is
9. $\left(0, \frac{\pi}{2}\right)$ The original inequality is equivalent to $2 \cos x>0$, i.e., $\cos x>0, x \in(0, \pi)$, so $x \in\left(0, \frac{\pi}{2}\right)$