\(A=\left(x+y\right)^2-3\left(x+y\right)+2017=\left(x+y\right)^2-2\dfrac{3}{2}\left(x+y\right)+\dfrac{9}{4}+\dfrac{8059}{4}\)
\(A=\left(x+y-\dfrac{3}{2}\right)^2+\dfrac{8059}{4}\ge\dfrac{8059}{4}\)
\(\Rightarrow A_{min}=\dfrac{8059}{4}\) khi \(x+y=\dfrac{3}{2}\)