(х+2у)^2+4х+5-4у-4ху=0

x² +4xy + 4y² + 4x + 5 - 4y - 4xy = x² + 4y² + 4x - 4y + 5=(x² + 4x)+ (4y²-4y)+5== x(x + 4) + 4y(y - 1) + 5