\[1)\ y = tg\ x \bullet ctg\ x = 1\]
\[x \neq \frac{\pi}{2} + \pi n\]
\[x \neq \pi n.\]
\[2)\ y = \sin x \bullet ctg\ x = \cos x\]
\[x \neq \pi n.\]
\[3)\ y = 2^{\text{tg\ x}}\]
\[tg\ x = 0:\]
\[y = 2^{0} = 1.\]
\[\text{tg\ x} = 1:\]
\[y = 2^{1} = 2.\]
\[\text{tg\ x} > 1:\]
\[2^{\text{tg\ x}} > 2^{1}\]
\[\text{\ y} > 2.\]
\[\text{tg\ x} < 1:\]
\[2^{- \infty} < 2^{\text{tg\ x}} < 2^{1}\]
\[0 < y < 1.\]
\[4)\ y = \sqrt{\text{ctg\ x}}\]
\[ctg\ x = 0:\]
\[y = \sqrt{0} = 0.\]
\[ctg\ x = 1:\]
\[y = \sqrt{1} = 1.\]
\[\text{ctg\ x} > 1:\]
\[\sqrt{\text{ctg\ x}} > \sqrt{1}\]
\[\text{\ y} > 1.\]
\[Область\ определения:\]
\[ctg\ x \geq 0.\]