1.
\(\Leftrightarrow sin\left(x-\frac{\pi}{3}\right)=-cos2x\)
\(\Leftrightarrow sin\left(x-\frac{\pi}{3}\right)=sin\left(2x-\frac{\pi}{2}\right)\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-\frac{\pi}{2}=x-\frac{\pi}{3}+k2\pi\\2x-\frac{\pi}{2}=\frac{4\pi}{3}-x+k2\pi\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{\pi}{6}+k2\pi\\x=\frac{11\pi}{18}+\frac{k2\pi}{3}\end{matrix}\right.\)
2.
\(\Leftrightarrow\frac{\sqrt{3}}{2}cosx-\frac{1}{2}sinx=0\)
\(\Leftrightarrow cos\left(x+\frac{\pi}{6}\right)=0\)
\(\Leftrightarrow x+\frac{\pi}{6}=\frac{\pi}{2}+k\pi\)
\(\Leftrightarrow x=\frac{\pi}{3}+k\pi\)
3.
\(\Leftrightarrow sin2x+1=2\left(\frac{1-cos2x}{2}\right)\)
\(\Leftrightarrow sin2x+cos2x=0\)
\(\Leftrightarrow\sqrt{2}sin\left(2x+\frac{\pi}{4}\right)=0\)
\(\Leftrightarrow2x+\frac{\pi}{4}=k\pi\)
\(\Leftrightarrow x=-\frac{\pi}{8}+\frac{k\pi}{2}\)
4. ĐKXĐ; ...
\(\Leftrightarrow\frac{sinx.cos2x}{cosx.sin2x}+1=0\)
\(\Leftrightarrow sinx.cos2x+cosx.sin2x=0\)
\(\Leftrightarrow sin3x=0\)
\(\Leftrightarrow3sinx-4sin^3x=0\)
\(\Leftrightarrow3-4sin^2x=0\)
\(\Leftrightarrow3-2\left(1-cos2x\right)=0\)
\(\Leftrightarrow cos2x=-\frac{1}{2}\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{\pi}{3}+k\pi\\x=-\frac{\pi}{3}+k\pi\end{matrix}\right.\)
5.
\(\Leftrightarrow sin\left(2cosx\right)=1\)
\(\Leftrightarrow2cosx=\frac{\pi}{2}+k2\pi\)
\(\Leftrightarrow cosx=\frac{\pi}{4}+k\pi\)
Do \(-1\le cosx\le1\Rightarrow-1\le\frac{\pi}{4}+k\pi\le1\)
Mà \(k\in Z\Rightarrow k=0\)
\(\Rightarrow cosx=\frac{\pi}{4}\)
\(\Leftrightarrow x=\pm arccos\left(\frac{\pi}{4}\right)+k2\pi\)
