ĐKXĐ: \(2cos^2x-1-sinx\ne0\Leftrightarrow cos2x-sinx\ne0\)
\(\Leftrightarrow cos2x\ne cos\left(\frac{\pi}{2}-x\right)\Leftrightarrow\left[{}\begin{matrix}2x\ne\frac{\pi}{2}-x+k2\pi\\2x\ne x-\frac{\pi}{2}+k2\pi\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x\ne\frac{\pi}{6}+\frac{k2\pi}{3}\\x\ne-\frac{\pi}{2}+k2\pi\end{matrix}\right.\)
Phương trình tương đương:
\(\frac{cosx-sin2x}{cos2x-sinx}=\sqrt{3}\)
\(\Leftrightarrow cosx-sin2x=\sqrt{3}cos2x-\sqrt{3}sinx\)
\(\Leftrightarrow sinx.\frac{\sqrt{3}}{2}+\frac{1}{2}cosx=sin2x.\frac{1}{2}+\frac{\sqrt{3}}{2}cos2x\)
\(\Leftrightarrow sin\left(x+\frac{\pi}{6}\right)=sin\left(2x+\frac{\pi}{3}\right)\)
\(\Leftrightarrow\left[{}\begin{matrix}2x+\frac{\pi}{3}=x+\frac{\pi}{6}+k2\pi\\2x+\frac{\pi}{3}=\pi-x-\frac{\pi}{6}+k2\pi\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=-\frac{\pi}{6}+k2\pi\\x=\frac{\pi}{6}+\frac{k2\pi}{3}\end{matrix}\right.\)
Kết hợp ĐKXĐ \(\Rightarrow x=-\frac{\pi}{6}+k2\pi\)
Kẻ \(MH\perp OA\), do \(\stackrel\frown{AM}=\frac{\pi}{6}=\frac{1}{3}\stackrel\frown{AB}\Rightarrow MH=\frac{1}{3}OB=\frac{1}{3}\)
\(\Rightarrow S_{OAM}=\frac{1}{2}MH.OA=\frac{1}{2}.\frac{1}{3}.1=\frac{1}{6}\left(đvdt\right)\)
