数学试题讲解

查看原题

已知

\tan (θ + \frac{π}{4}) = \frac{1}{2} \tan θ - \frac{7}{2}

, 则

\cos 2 θ =

- \frac{1}{2}

\frac{1}{2}

- \frac{4}{5}

\frac{4}{5}