\textbf{122.} For the graph of $f(x) = \cos^2 x - 2\cos x$; $x \in [0, 2\pi]$, at which base point is the inflection point and local minimum?
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(1) $\left(\dfrac{\pi}{2}, \dfrac{2\pi}{3}\right)$ \hfill (2) $\left(\pi, \dfrac{4\pi}{3}\right)$ \hfill (3) $\left(\dfrac{2\pi}{3}, \pi\right)$ \hfill (4) $\left(\dfrac{4\pi}{3}, \dfrac{3\pi}{2}\right)$
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