原式=3y^2-y-2x^2+2x=3(y^2-1/3y+1/36)-2(x^2-x+1/4)+5/12=3(y-1/6)^2-2(x-1/2)^2+5/12代入x=1，y=-1得 原式=4
=2x-y+4y-2x-2x+2y=5y-2x=-5-2=-7
