Решебник по алгебре и начала математического анализа 11 класс Колягин Задание 28

\[y = \cos x;\ \ \ x \in \lbrack 0;\ 3\pi\rbrack.\]

\[1)\ \cos x = 0:\]

\[\ x_{1} = \frac{\pi}{2},\ \ \ x_{2} = \frac{3\pi}{2},\ \ \ x_{3} = \frac{5\pi}{2}.\]

\[\cos x = 1:\]

\[x_{1} = 0,\ \ \ x_{2} = 2\pi.\]

\[\cos x = - 1:\ \]

\[x_{1} = \pi,\ \ \ x_{2} = 3\pi.\]

\[2)\ \cos x > 0:\]

\[0 \leq x < \frac{\pi}{2}\]

\[\frac{3\pi}{2} < x < \frac{5\pi}{2}.\]

\[3)\ \cos x < 0:\ \]

\[\frac{\pi}{2} < x < \frac{3\pi}{2}\]

\[\frac{5\pi}{2} < x \leq 3\pi.\]