In an isosceles triangle ABC with $\overline { \mathrm { AB } } = \overline { \mathrm { AC } }$, let $\angle \mathrm { A } = \alpha , \angle \mathrm { B } = \beta$. If $\tan ( \alpha + \beta ) = - \frac { 3 } { 2 }$, what is the value of $\tan \alpha$? [3 points]\\
(1) $\frac { 5 } { 2 }$\\
(2) $\frac { 12 } { 5 }$\\
(3) $\frac { 23 } { 10 }$\\
(4) $\frac { 11 } { 5 }$\\
(5) $\frac { 21 } { 10 }$