a/
\(30\left(1-sin^23x\right)-29sin3x-23=0\)
\(\Leftrightarrow-30sin^23x-29sin3x+7=0\)
\(\Rightarrow\left[{}\begin{matrix}sin3x=\frac{1}{5}\\sin3x=-\frac{7}{6}< -1\left(l\right)\end{matrix}\right.\)
\(\Rightarrow sin3x=sina\) (với \(sina=\frac{1}{5}\))
\(\Rightarrow\left[{}\begin{matrix}3x=a+k2\pi\\3x=\pi-a+k2\pi\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{a}{3}+\frac{k2\pi}{3}\\x=\frac{\pi}{3}-\frac{a}{3}+\frac{k2\pi}{3}\end{matrix}\right.\)
b/
\(1-cos^2\frac{x}{2}-2cos\frac{x}{2}+2=0\)
\(\Leftrightarrow-cos^2\frac{x}{2}-2cos\frac{x}{2}+3=0\)
\(\Leftrightarrow\left[{}\begin{matrix}cos\frac{x}{2}=1\\cos\frac{x}{2}=-3< -1\left(l\right)\end{matrix}\right.\)
\(\Rightarrow\frac{x}{2}=k2\pi\Rightarrow x=k4\pi\)
