\(VT\ge\frac{1}{2}\left(sin^2x+cos^2x+\frac{1}{sin^2x}+\frac{1}{cos^2x}\right)^2\)
\(VT\ge\frac{1}{2}\left(1+\frac{1}{sin^2x}+\frac{1}{cos^2x}\right)^2\ge\frac{1}{2}\left(1+\frac{4}{sin^2x+cos^2x}\right)=\frac{25}{2}\)
\(VP=\frac{9}{2}-\left(sin^2y-2siny+1\right)=\frac{9}{2}-\left(siny-1\right)^2\le\frac{9}{2}< VT\)
Phương trình đã cho luôn luôn vô nghiệm