Considering only the principal values of the inverse trigonometric functions, the domain of the function \( f(x)=\cos^{-1}\!\left(\dfrac{x^2-4x+2}{x^2+3}\right) \) is:
\( \left(-\infty, \ \dfrac{1}{4}\right] \)
\( \left[-\dfrac{1}{4}, \ \infty\right) \)
\( \left(-\dfrac{1}{3}, \ \infty\right) \)
\( \left(-\infty, \ \dfrac{1}{3}\right] \)