\[\boxed{\mathbf{694}\mathbf{.}}\]
\[1)\ y = \sqrt{\sin x + 1}\]
\[\sin x + 1 \geq 0\]
\[\sin x \geq - 1\]
\[при\ любом\ x.\]
\[Ответ:\ \ x \in R.\]
\[2)\ y = \sqrt{\cos x - 1}\]
\[\cos x - 1 \geq 0\]
\[\cos x \geq 1\]
\[\cos x = 1\]
\[x = \arccos 1 + 2\pi n = 2\pi n.\]
\[Ответ:\ \ x = 2\pi n.\]
\[3)\ y = \lg{\sin x}\]
\[\sin x > 0\]
\[\arcsin 0 + 2\pi n < x <\]
\[< \pi - \arcsin 0 + 2\pi n.\]
\[Ответ:\ \ 2\pi n < x < \pi + 2\pi n.\]
\[4)\ y = \sqrt{2\cos x - 1}\]
\[2\cos x - 1 \geq 0\]
\[2\cos x \geq 1\]
\[\cos x \geq \frac{1}{2}\]
\[- \arccos\frac{1}{2} + 2\pi n \leq x \leq\]
\[\leq \arccos\frac{1}{2} + 2\pi n.\]
\[Ответ:\ \]
\[- \frac{\pi}{3} + 2\pi n \leq x \leq \frac{\pi}{3} + 2\pi n.\]
\[5)\ y = \sqrt{1 - 2\sin x}\]
\[1 - 2\sin x \geq 0\]
\[- 2\sin x \geq - 1\]
\[\sin x \leq \frac{1}{2}\]
\[- \pi - \arcsin\frac{1}{2} + 2\pi n \leq x \leq \arcsin\frac{1}{2} + 2\pi n\]
\[- \pi - \frac{\pi}{6} + 2\pi n \leq x \leq \frac{\pi}{6} + 2\pi n.\]
\[Ответ:\ \]
\[- \frac{7\pi}{6} + 2\pi n \leq x \leq \frac{\pi}{6} + 2\pi n.\]
\[6)\ y = \ln{\cos x}\]
\[\cos x > 0\]
\[- \arccos 0 + 2\pi n < x < \arccos 0 + 2\pi n.\]
\[Ответ:\ \]
\[- \frac{\pi}{2} + 2\pi n < x < \frac{\pi}{2} + 2\pi n.\]