\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Find the exact value of \(\cos \theta\) if \(\sin \theta = \dfrac{1}{\sqrt{2}}\) and \(\dfrac{\pi}{2} < \theta < \dfrac{3\pi}{2}\).
\(\cos \theta =\)