Consider the function
$$f ( x ) = \sin 2 x - 3 ( \sin x + \cos x )$$
on the interval $- \dfrac { \pi } { 3 } \leqq x \leqq \dfrac { \pi } { 3 }$.
(1) Let $t = \sin x + \cos x$. Find the range of the values which $t$ can take.
(2) The function $f ( x )$ takes its minimum value $\mathbf { E } - \mathbf { F } \sqrt{\mathbf{G}}$ at $x = \dfrac { \mathbf { H } } { \mathbf { I } }$.