Let \( a \) and \( b \) be real constants such that the function \( f \) defined by be differentiable on \( \mathbb{R} \). Then, the value of \( \displaystyle \int_{-2}^{2} f(x)\,dx \) equals.
\(17\)
\(\dfrac{19}{6}\)
\(\dfrac{15}{6}\)
\(21\)