Question

min x^2 + 4y^2 - 4xy + 2x - 4y + 9

Answer 1

Đặt \(P=x^2+4y^2-4xy+2x-4y+9\)

\(P=\left(x-2y\right)^2+2\left(x-2y\right)+1+8\)

\(P=\left(x-2y+1\right)^2+8\ge8\)

\(P_{min}=8\) khi \(x-2y+1=0\)