\(A=\frac{3m-2n}{3m+2n}\)
\(\Leftrightarrow A^2=\frac{(3m-2n)^2}{(3m+2n)^2}=\frac{9m^2-12mn+4n^2}{9m^2+12mn+4n^2}=\frac{20mn-12mn}{20mn+12mn}=\frac{8mn}{32mn}=\frac 1 4\)
\(\Rightarrow |A|=\frac1 2\)
\(2n<3n<0 \Rightarrow \left\{\begin{matrix}
3n-2n>0\\ 3n+2n<0
\end{matrix}\right. \Rightarrow A<0\)
\(\Rightarrow A=\frac{-1} 2\)
Chúc bạn học tốt!