\(y=1-2\sin^2x-\sin x+3=-2\sin^2x-\sin x+4\)
\(\sin x=t;t\in\left[-1;1\right]\)
Xét hàm f(t) trên [-1;1]
\(f\left(-1\right)=-2+1+4=3\)
\(f\left(1\right)=-2-1+4=1\)
\(f\left(-\frac{1}{4}\right)=-2.\frac{1}{16}+\frac{1}{4}+4=\frac{33}{8}\)
\(\Rightarrow\left\{{}\begin{matrix}y_{max}=\frac{33}{8};"="\Leftrightarrow\sin x=-\frac{1}{4}\Rightarrow x=...\\y_{min}=1;"="\Leftrightarrow\sin x=1\end{matrix}\right.\)