If \(\tan 15^\circ + \dfrac{1}{\tan 75^\circ} + \dfrac{1}{\tan 105^\circ} + \tan 195^\circ = 2a\), Then the value of \(\left(a + \dfrac{1}{a}\right)\) is:
\(5 - \dfrac{3}{2}\sqrt{3}\)
\(4 - 2\sqrt{3}\)
\(2\)
\(4\)