\(y=1-2sin^22x+2sin^42x\)
\(y=2\left(sin^22x-\frac{1}{2}\right)^2+\frac{1}{2}\ge\frac{1}{2}\)
\(y_{min}=\frac{1}{2}\) khi \(sin^22x=\frac{1}{2}\)
\(y=2sin^22x\left(sin^22x-1\right)+1\)
Do \(0\le sin^22x\le1\Rightarrow2sin^22x\left(sin^22x-1\right)\le0\)
\(\Rightarrow y\le1\Rightarrow y_{max}=1\) khi \(sin^22x=1\)