chị dua vao ct tinh 2 nghiem roi tinh dc A sau do tim m de Amin
dai lam e k lam dau
\(\Delta'=\left(m-1\right)^2-\left(m-3\right)=m^2-3m+4=\left(m-\frac{3}{2}\right)^2+\frac{7}{4}>0\)
\(A=\left(x_1+x_2\right)^2-2x_1x_2=4\left(m-1\right)^2-2\left(m-3\right)=4m^2-10m+10=\left(2m-\frac{5}{2}\right)^2+\frac{15}{4}\)
A min = 15/4 khi 2m =5/2 hay m = 5/4