Question

Answer 1

5:

\(A=-2\left(x^2+y^2+1-2xy-2x+2y\right)-8y^2+8y+2020\)

\(=-2\left[\left(x-y\right)^2-2\left(x-y\right)+1\right]-8y^2+8y+2020\)

\(=-2\left(y-x+1\right)^2-8\left(y^2-y+\dfrac{1}{4}\right)+2022\)

\(=-2\left(x+y-1\right)^2-8\left(y-\dfrac{1}{2}\right)^2+2022< =2022\)

Dấu = xảy ra khi y=1/2 và x=-y+1=-1/2+1=1/2