数学试题讲解

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已知

\sin (α - β) = \frac{1}{3}, \cos α \sin β = \frac{1}{6}

, 则

\cos (2 α + 2 β) =

\frac{7}{9}

\frac{1}{9}

- \frac{1}{9}

- \frac{7}{9}