Bài 1: a) Txđ: $D=\mathbb R$
b) Đk: $x+2\ne0\Rightarrow x\ne-2$
Txđ: $D=\mathbb R\backslash\{-2\}$
c) Đk: $x+4\ge0\Rightarrow x\ge-4$
Txđ: $D=[-4;+\infty)$
d) Đk: $\left\{ \begin{array}{l} \sin x\ne0 \\\cos x\ne0\end{array} \right .\Rightarrow \left\{ \begin{array}{l} x\ne k\pi \\ x\ne\dfrac{\pi}{2}+k\pi \end{array} \right .$
$\Rightarrow D=\mathbb R\backslash\{k\pi;\dfrac{\pi}{2}+k\pi,(k\in\mathbb Z)\}$
e) $\cos 2x\ne0\Rightarrow 2x\ne \dfrac{\pi}{2}+k\pi$
$\Rightarrow x\ne\dfrac{\pi}{4}+k\dfrac{\pi}{2}$
f) $2-\sin x\ge0$
Do $-1\le\sin x\le1$ $\forall x$
$\Rightarrow 2-\sin x>0$ $\forall x$
Txđ: $D=\mathbb R$
g) Đk: $1-\sin x\ne0\Rightarrow \sin x\ne1$
$\Rightarrow x\ne\dfrac{\pi}{2}+k2\pi$ $(k\in\mathbb Z)$
Txđ: $D=\mathbb R\backslash\{\dfrac{\pi}{2}+k2\pi(k\in\mathbb Z)\}$
h) đk $\cos(x+\dfrac{\pi}{4})\ne 0$
$\Rightarrow x+\dfrac{\pi}{4}\ne\dfrac{\pi}{2}+k\pi$
i) Đk: $\sin(2x-\dfrac{\pi}{3})\ne0$
$\Rightarrow 2x-\dfrac{\pi}{3}\ne k\pi$
