4) cos x = 1 3 9) cos = √2 2

• \(x = \pm arccos \frac{1}{3} + 2\pi n\)

Ответ: \(x = \pm arccos \frac{1}{3} + 2\pi n\)

• \(\frac{x}{3} = \pm arccos \frac{\sqrt{2}}{2} + 2\pi n\)
• \(\frac{x}{3} = \pm \frac{\pi}{4} + 2\pi n\)
• \(x = \pm \frac{3\pi}{4} + 6\pi n\)

Ответ: \(x = \pm \frac{3\pi}{4} + 6\pi n\)