Chọn khẳng định đúng A. tan (a - b) = (tan a - tan b)

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

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

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

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