Question

[Hồng Miêu]

Giúp em câu 3,4,5. Em xin cảm ơn.

Answer 1

[Nguyễn Việt Lâm]

ĐKXĐ:

3.

\(cos\left(3x-\dfrac{\pi}{4}\right)\ne0\Leftrightarrow3x-\dfrac{\pi}{4}\ne\dfrac{\pi}{2}+k\pi\)

\(\Leftrightarrow3x\ne\dfrac{3\pi}{4}+k\pi\Rightarrow x\ne\dfrac{\pi}{4}+\dfrac{k\pi}{3}\)

4.

\(sin\left(2x+\dfrac{\pi}{6}\right)\ne0\Leftrightarrow2x+\dfrac{\pi}{6}\ne k\pi\)

\(\Rightarrow x\ne-\dfrac{\pi}{12}+\dfrac{k\pi}{2}\)

5.

\(\left\{{}\begin{matrix}cosx\ne0\\sin3x\ne0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ne\dfrac{\pi}{2}+k\pi\\3x\ne k\pi\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x\ne\dfrac{\pi}{2}+k\pi\\x\ne\dfrac{k\pi}{3}\end{matrix}\right.\)