\(A=x^2-4xy+4y^2+x^2+2x+1+2018\)

\(A=\left(x-2y\right)^2+\left(x+1\right)^2+2018\ge2018\)

\(A_{min}=2018\) khi \(\left\{{}\begin{matrix}x=-1\\y=-\frac{1}{2}\end{matrix}\right.\)

\(B=-\left(4x^2+4xy+y^2\right)-\left(x^2-6x+9\right)+2029\)

\(B=-\left(2x+y\right)^2-\left(x-3\right)^2+2029\le2029\)

\(B_{max}=2029\) khi \(\left\{{}\begin{matrix}x=3\\y=-6\end{matrix}\right.\)

\(N = 5x^2 + 2y^ 2 + 4xy - 2x + 4y + 2015\)

\(N = ( 4x^ 2 + 4xy + y ^ 2 ) + ( x^2 - 2x + 1 )+\)

\(( y^2 + 4y + 4 ) + 2010\)

\(N = ( 2x + y )^2 + ( x - 1 )^2 + ( y + 2 )^2 + 2010\)

\(\ge\)\(2010\)

\(Dấu " = " xảy ra \)\(\Leftrightarrow\) \(2x + y = 0 và\)\(x - 1 = 0 và y + 2 = 0\)

\(\Rightarrow\)\(x = 1 và y = - 2\)

\(Min N = 2010\)\(\Leftrightarrow\)\(x = 1 và y = - 2\)

B= \(4x^2+4xy+y^2+x^2-2x+1+y^2+4y+4+15\)

= \(\left(2x+y\right)^2+\left(x-1\right)^2+\left(y+2\right)^2+15\ge15\)

=> GTNN của B là 15

F = 5x² + 2y² + 4xy - 2x + 4y + 8

F = ( 4x² + 4xy + y² ) + ( x² - 2x + 1 ) + ( y² + 4y + 4 ) + 3

F = ( 2x + y )² + ( x - 1 )² + ( y + 2 )² + 3

\(\hept{\begin{cases}\left(2x+y\right)^2\\\left(x-1\right)^2\\\left(y+2\right)^2\end{cases}}\ge0\forall x,y\Rightarrow\left(2x+y\right)^2+\left(x-1\right)^2+\left(y+2\right)^2+3\ge3\forall x,y\)

Đẳng thức xảy ra <=> \(\hept{\begin{cases}2x+y=0\\x-1=0\\y+2=0\end{cases}}\Rightarrow\hept{\begin{cases}x=1\\y=-2\end{cases}}\)

Vậy MinF = 3 <=> x = 1 , y = -2

G = 5x² + 5y² + 8xy + 2y + 2020

= x² + ( 4x² + 8xy + 4y² ) + ( y² + 2y + 1 ) + 2019

= x² + ( 2x + 2y )² + ( y + 1 )² + 2019

\(\hept{\begin{cases}x^2\\\left(2x+2y\right)^2\\\left(y+1\right)^2\end{cases}}\ge0\forall x,y\Rightarrow x^2+\left(2x+2y\right)^2+\left(y+1\right)^2+2019\ge2019\forall x,y\)

Tuy nhiên đẳng thức không xảy ra :P

a=(2x+y)^2+(x-1)^2+(y+2)^2+2021-5=2016

Amin=2016