1.
ĐK: $3x-5\ge 0$
$\Leftrightarrow x\ge \dfrac{5}{3}$
$\to D=[\dfrac{5}{3};+\infty)$
2.
ĐK: $\cos(2x-\dfrac{\pi}{4})\ne 0$
$\Leftrightarrow 2x-\dfrac{\pi}{4}\ne \dfrac{\pi}{2}+k\pi$
$\Leftrightarrow x\ne \dfrac{3\pi}{8}+\dfrac{k\pi}{2}$
$\to D=\mathbb{R}$ \ $\{\dfrac{3\pi}{8}+\dfrac{k\pi}{2}\}$
3.
ĐK: $x^2\ne \dfrac{\pi}{3}$
$\Leftrightarrow x\ne \pm\dfrac{\sqrt{\pi}}{\sqrt3}$
$\to D=\mathbb{R}$ \ $\{\pm \dfrac{\sqrt{\pi}}{\sqrt3}\}$
4. (Bạn ghi lại mẫu nha)
5.
ĐK: $\sin(x+3)\ne 0$
$\Leftrightarrow x\ne -3+k\pi$
$\to D=\mathbb{R}$ \ $\{-3+k\pi\}$
