m=x^2-4xy+6y^2-4x-4y
=(3x^2/4-4xy+16y^2/3)+(x^2/4-4x+16)+(2y^2/3-4y+6)-22
=3(x-8y/3)^2/4+(x-8)^2/4+2(y-3)^2/3-22>=-22,
所以当x=8,y=3时,m最小为-22.