\(A=\left(4x^2+25y^2+9-20xy-12x+30y\right)+\left(9x^2+6x+1\right)-2\)
\(A=\left(2x-5y-3\right)^2+\left(3x+1\right)^2-2\ge-2\)
\(A_{min}=-2\) khi \(\left\{{}\begin{matrix}x=-\frac{1}{3}\\y=-\frac{11}{15}\end{matrix}\right.\)
\(B=\left(x^2-3x+\frac{9}{4}\right)+\left(y^2-4y+4\right)-\frac{8105}{4}\)
\(B=\left(x-\frac{3}{2}\right)^2+\left(y-2\right)^2-\frac{8105}{4}\ge-\frac{8105}{4}\)
\(B_{min}=-\frac{8105}{4}\) khi \(\left\{{}\begin{matrix}x=\frac{3}{2}\\y=2\end{matrix}\right.\)
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