10. Given the complex number $z$ satisfies $\left|2 z+\frac{1}{z}\right|=1$, then the principal value of the argument of $z$ is $\qquad$
10. $\left[\frac{\pi}{2}-\frac{1}{2} \arccos \frac{3}{4}, \frac{\pi}{2}+\frac{1}{2} \arccos \frac{3}{4}\right] \cup\left[\frac{3 \pi}{2}-\frac{1}{2} \arccos \frac{3}{4}, \frac{3 \pi}{2}+\frac{1}{2} \arccos \frac{3}{4}\right]$.