\(\left(x^2-2xy+y^2-2x+2y+1\right)+\left(x^2+6x+\frac{9}{4}\right)+\left(5-\left(1+\frac{9}{4}\right)\right)=\left(x-y-1\right)^2+\left(x+1\right)^2+\frac{25}{4}\ge\frac{25}{4}\)
đẳng thúc khi :\(\left\{\begin{matrix}x+\frac{3}{2}=0\\x-y-1=0\end{matrix}\right.\)=> x=...;y=...