-3(1/2x^2-2xy+y^2)+1/2(2x^2-xy-2y^2)
=-3/2x^2+6xy-3y^2+x^2-1/2xy-y^2
=-1/2x^2+11/2xy-4y^2你把题目看错了吧。。你写错了第一项是x^2我没写错，，哦 -3(1/2x-2xy+y^2)+1/2(2x^2-xy-2y^2)=-3/2x+6xy-3y^2+x^2-1/2xy-y^2=x^2-3/2x+11/2xy-4y^2