(x-y)^4=x^4+y^4+6x^2y^2-4x^3y-4y^3xx^4-2x^2y^2-4xy^3+4x^3+y^2（4x^2+3/4y^2)=1/4[(4x^4+4y^4+24x^2y^2-16x^3y-16y^3x)-16x^2y^2+16x^3y+16x^3-y^4]=1/4[4(x-y)^4-16x^2y^2+16x^3y+16x^3-y^4]=(x-y)^4-4x^2y^2+4x...