a, Ta có: \(\forall m\) hệ có nghiệm duy nhất là: \(\left\{{}\begin{matrix}x=\frac{2m+5}{m^2+3}\\y=\frac{5m-6}{m^2+3}\end{matrix}\right.\)
b, Có: \(x+y=1-\frac{m^2}{m^2+3}\)
\(\Leftrightarrow\frac{2m+5}{m^2+3}+\frac{5m-6}{m^2+3}=1-\frac{m^3}{m^2+3}\)
\(\Leftrightarrow m=\frac{7}{4}\)
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