Помогите пожалуйста 30 баллов

1)
$y = \sqrt{\cos 3x}\\\\ y' =(\sqrt{\cos 3x})' * (\cos 3x)'\\\\ (\cos 3x)' = (\cos 3x)' * (3x)' = -\sin 3x * 3 = -3\sin 3x\\\\ y' = \frac{1}{2\sqrt{\cos 3x}} * (-3\sin 3x) = -\frac{3\sin 3x}{2\sqrt{\cos 3x}}\\$

2)
$y = \frac{x}{5} \tan 3x\\\\ y' = \frac{1}{5}*(x'* \tan 3x + x * (\tan 3x)')\\\\ (\tan 3x)' = \frac{3}{\cos^2x}\\\\ y' = \frac{\tan 3x + \frac{3x}{\cos^2x}}{5}\\\\$

3)
$f(x) = 4\cos \frac{x}{2} - x\sqrt{2}\\\\ f'(x) = -2\sin \frac{x}{2} - \sqrt{2}\\\\ -2\sin \frac{x}{2} - \sqrt{2} \ \textless \ 0\\ -2\sin \frac{x}{2} \ \textless \ \sqrt{2}\\ \sin \frac{x}{2} \ \textgreater \ -\frac{\sqrt{2}}{2}\\\\ \frac{x}{2} \in (\frac{5\pi}{4} + 2\pi n; \pi - \frac{5\pi}{4}+2\pi n)\\\\ \frac{x}{2} \in (\frac{5\pi}{4} + 2\pi n;-\frac{\pi}{4}+2\pi n)\\\\ x \in (\frac{5\pi}{2} + 4\pi n;-\frac{\pi}{2}+4\pi n)\\$