Вычислите \(\ctg\alpha\) , если \(\cos\alpha = -\frac{1}{3}\) и \(\frac{\pi}{2} < \alpha < \pi\) .
\(-\frac{\sqrt{2}}{4}\)
\(\frac{\sqrt{2}}{4}\)
\(-\frac{1}{2}\)
\(\frac{1}{2}\)