Let \( f:\mathbb{R}\to\mathbb{R} \) be a function defined as .If \( f \) is continuous at \( x=0 \), then the value of \( a+b \) is equal to:
\( -\dfrac{5}{2} \)
\( -\dfrac{3}{2} \)
\( -2 \)
\( -3 \)