Đáp án + Giải thích các bước giải:
`cos(2x+ π/6) = 1/4 `
`<=>`\(\left[ \begin{array}{l}2x+\dfrac{\pi}{6}=\arccos(\dfrac{1}{4})+k2\pi\\2x+\dfrac{\pi}{6}=-\arccos(\dfrac{1}{4})+k2\pi\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}2x=-\dfrac{\pi}{6}+\arccos(\dfrac{1}{4})+k2\pi\\2x=-\dfrac{\pi}{6}-\arccos(\dfrac{1}{4})+k2\pi\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=-\dfrac{\pi}{12}+\dfrac{1}{2}\arccos(\dfrac{1}{4})+k\pi\\x=-\dfrac{\pi}{12}-\dfrac{1}{2}\arccos(\dfrac{1}{4})+k\pi\end{array} \right.\)`(kinZZ)`
