câu A thiếu đề
B=\(x^2-2x+2017=\left(x-1\right)^2+2016>=2016\)
Min B=2016 khi x-1=0<=>x=1
+)D=\(-2x^2+4x+2017=-2\left(x^2-2x+1\right)+2019=-2\left(x-1\right)^2+2019< =2019\)
=>Max D=2019, dấu '=' xảy ra khi x-1=0<=>x=1
\(A=x^2+2xy+3y^2-4y+2017\)
\(A=\left(x^2+2xy+y^2\right)+\left(2y^2-4y+2\right)+2015\)
\(A=\left(x^2+2xy+y^2\right)+2\left(y^2-2y+1\right)+2015\)
\(A=\left(x+y\right)^2+2\left(y-1\right)^2+2015\ge2015\)
Vậy Amin=2015 <=> x=-1 và y=1