Vì \(\left\{{}\begin{matrix}-1\le sinx\le1\\-1\le cosx\le1\end{matrix}\right.\)
\(\Rightarrow n=0\le y=\left|cos^2x-2sinx-1\right|\le\left|1-2.\left(-1\right)-1\right|=2=m\)
\(\Rightarrow\left\{{}\begin{matrix}m=2\\n=0\end{matrix}\right.\)
\(2m+3n=2.2+3.0=4\)