Let \( f : \mathbb{R} \to \mathbb{R} \) be defined by \( f(x) = \dfrac{x^{2} - 3x - 6}{x^{2} + 2x + 4} \). Then which of the following statements is (are) TRUE?
\( f \) is decreasing in the interval \( (-2,-1) \)
\( f \) is increasing in the interval \( (1,2) \)
\( f \) is onto
Range of \( f \) is \( \left[ -\dfrac{3}{2}, 2 \right] \)