1) 2 cos 3 x = 2) (2/5) <1

$1)\; \; 2cos3x=\sqrt3\\\\cos3x=\frac{\sqrt3}{2}\\\\3x=\pm \frac{\pi}{6}+2\pi n,\; n\in Z\\\\x=\pm \frac{\pi}{18}+\frac{2\pi n}{3}\; ,\; n\in Z\\$

$2)\; \; \frac{2}{5}x^2-5+6\ \textless \ 1\\\\\frac{2}{5}x^2\ \textless \ 0\; \; net\; reshenij\; ,\; t.k.\; x^2 \geq 0\\$

3) $(\frac{2}{5})^{x^2-5x+6}<1;1=(\frac{2}{5})^0$

$x^2-5x+6\ \textgreater \ 0\\\\x_1=2,x_2=3\\\\+++(2)---(3)+++\\\\x\in(-\infty, 2)\cup(3,+\infty)$