数学试题讲解

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若

\cos α - \sin α = - \frac{1}{2}

, 则

\frac{\sin α \cos α}{\tan^{2} (α - \frac{π}{4})} =

- \frac{21}{4}

\frac{21}{4}

- \frac{21}{8}

\frac{21}{8}