The sum of the infinite series \( \cot^{-1}\!\left(\dfrac{7}{4}\right)+\cot^{-1}\!\left(\dfrac{19}{4}\right)+\cot^{-1}\!\left(\dfrac{39}{4}\right)+\cot^{-1}\!\left(\dfrac{67}{4}\right)+\ldots \) is:
\( \dfrac{\pi}{2}-\cot^{-1}\!\left(\dfrac{1}{2}\right) \)
\( \dfrac{\pi}{2}-\tan^{-1}\!\left(\dfrac{1}{2}\right) \)
\( \dfrac{\pi}{2}+\cot^{-1}\!\left(\dfrac{1}{2}\right) \)
\( \dfrac{\pi}{2}+\tan^{-1}\!\left(\dfrac{1}{2}\right) \)