-(2xy-y^2+1/2x^2)-2(1/3xy+1/4y^2-x^2)

问题描述:

-(2xy-y^2+1/2x^2)-2(1/3xy+1/4y^2-x^2)

-(2xy-y^2+1/2x^2)-2(1/3xy+1/4y^2-x^2)
=-2xy+y^2-1/2x^2-2/3xy-1/2y^2+2x^2
=3x^2/2-8xy/3+y^2/2