$\begin{array}{l}
c,A = {x^2} + 2{y^2} - 2xy - 6x + 8y + 11\\
\Rightarrow A = {x^2} + {y^2} + 9 - 2xy - 6x + 6y + {y^2} + 2y + 1 + 1\\
\Rightarrow A = {\left( {3 - x + y} \right)^2} + {\left( {y + 1} \right)^2} + 1 \ge 1\\
\min A = 1khiy = - 1,x = 2\\
d,B = {x^2} + \frac{5}{4}{y^2} + xy - 3y...