\(A=\left(x-2y+1\right)^2+\left[2\left(x-2y+1\right)+3\right]^2\)
\(=\left(x-2y+1\right)^2+4\left(x-2y+1\right)^2+12\left(x-2y+1\right)+9\)
\(=5\left(x-2y+1\right)^2+12\left(x-2y+1\right)+9\)
\(=5\left(x-2y+1+\frac{6}{5}\right)^2+\frac{9}{5}\ge\frac{9}{5}\)