\[\boxed{\mathbf{425.}}\]
\[\ a = x + 2\pi k\]
\[1)\ a = 9,8\pi:\]
\[a = 1,8\pi + 8\pi = \frac{18}{10}\pi + 8\pi =\]
\[= \frac{9\pi}{5} + 2\pi \bullet 4\]
\[Ответ:\ \ x = \frac{9\pi}{5};\ \ k = 4.\]
\[2)\ a = 7\frac{1}{3}\pi:\]
\[a = 1\frac{1}{3}\pi + 6\pi = \frac{4\pi}{3} + 2\pi \bullet 3\]
\[Ответ:\ \ x = \frac{4\pi}{3};\ \ k = 3.\]
\[3)\ a = \frac{11}{2}\pi:\]
\[a = \frac{3\pi}{2} + \frac{8\pi}{2} = \frac{3\pi}{2} + 4\pi =\]
\[= \frac{3\pi}{2} + 2\pi \bullet 2\]
\[Ответ:\ \ x = \frac{3\pi}{2};\ \ k = 2.\]
\[4)\ a = \frac{17}{3}\pi:\]
\[a = \frac{5\pi}{3} + \frac{12\pi}{3} = \frac{5\pi}{3} + 4\pi =\]
\[= \frac{5\pi}{3} + 2\pi \bullet 2\]
\[Ответ:\ \ x = \frac{5\pi}{3};\ \ k = 2.\]