Công thức nào dưới đây SAI A. tan (a - b)

$\tan \left( {a - b} \right) = \frac{{\tan a - \tan b}}{{1 + \tan a\tan b}}$.

\[\cos a\cos b = \frac{1}{2}\left[ {{\text{cos}}\left( {a - b} \right) + {\text{cos}}\left( {a + b} \right)} \right]\].

\[\sin a\cos b = \frac{1}{2}\left[ {{\text{sin}}\left( {a - b} \right) + {\text{sin}}\left( {a + b} \right)} \right]\].

\[\sin a\sin b = \frac{1}{2}\left[ {{\text{cos}}\left( {a - b} \right) + {\text{cos}}\left( {a + b} \right)} \right]\].