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

• \(-\frac{\sqrt{2}}{4}\)
• \(\frac{\sqrt{2}}{4}\)
• \(-\frac{1}{2}\)
• \(\frac{1}{2}\)