\textbf{118.} From the point $A(2,-1)$, two tangent lines to the curve $y = \dfrac{1}{2}x^2 - x$ are drawn. What is the angle between these two tangent lines?
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(1) $\dfrac{\pi}{4}$ \hfill (2) $\dfrac{\pi}{3}$ \hfill (3) $\dfrac{\pi}{2}$ \hfill (4) $\tan^{-1}2$
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