The angle between vector A and (A - B) is

$\text{ Angle between }\overrightarrow{\mathrm{A}}\text{ and }\overrightarrow{\mathrm{B}},\theta =60°$

$\text{ Angle betwenn }\overrightarrow{\mathrm{A}}\text{ and }\overrightarrow{\mathrm{A}}-\overrightarrow{\mathrm{B}}$

$\tan \alpha =\frac{\mathrm{Bsin}\theta }{\mathrm{A}-\mathrm{Bcos}\theta }$

$=\frac{\mathrm{B}\sqrt{\frac{3}{2}}}{ \mathrm{A}-\mathrm{B}\times \frac{1}{2}2}$

$\tan \alpha =\frac{\sqrt{3}B}{2A-B}$