-5(xy—6x²+7y)+3(2xy—x²+2y)=-5xy+30x^2-35y+6xy-3x^2+6y=xy+27x^2-29y=1/2 * (-1) +27(1/闷春散2)^2-29*(-1)=-1/2+27/4+29=25/4+29=35又 1/蚂氏森颤4
-5(xy—6x²型旁贺袜+7y)+3(2xy—x²+2y)卜拍橡=33x²+xy-29y=33/4-1/2+29=36又4分之3