(-x^2+3xy-0.5y^2)-(0.5x^2+4xy-1.5y^2)=-0.5x^2+( )+y^2

问题描述:

(-x^2+3xy-0.5y^2)-(0.5x^2+4xy-1.5y^2)=-0.5x^2+( )+y^2

(-x^2+3xy-0.5y^2)-(0.5x^2+4xy-1.5y^2)
=-x^2+3xy-0.5y^2-0.5x^2-4xy+1.5y^2
=-1.5x^2-xy+y^2
所以填-xy