Đáp án:
Giải thích các bước giải:
a) ĐK: `2x+\frac{\pi}{4} \ne k\pi`
`⇔ x \ne \frac{-\pi}{8}+\frac{k\pi}{2}\ (k \in \mathbb{Z})`
`D=\mathbb{R} \\ {\frac{-\pi}{8}+\frac{k\pi}{2}\ (k \in \mathbb{Z})}`
b) `D=\mathbb{R} \\ {k\pi\ (k\in \mathbb{Z})}`
c) ĐK: `2x-\frac{\pi}{6} \ne \frac{\pi}{2}+k\pi`
`⇔ x \ne \frac{\pi}{3}+\frac{k\pi}{2}\ (k \in \mathbb{Z})`
`D=\mathbb{R} \\ {\frac{\pi}{3}+\frac{k\pi}{2}\ (k \in \mathbb{Z})}`
d) `ĐK: cos x \ne 1`
`⇔ x \ne k2\pi\ (k \in \mathbb{Z})`
`D=\mathbb{R} \\ {k2\pi\ (k \in \mathbb{Z})}`
