已知x-2y=1/2,xy=2,求-x^4y^2+4x^3y^3-4x^2y^4的值
问题描述:
已知x-2y=1/2,xy=2,求-x^4y^2+4x^3y^3-4x^2y^4的值
答
-x^4y^2+4x^3y^3-4x^2y^4
=-x^2y^2(x^2-4xy+4y^2)
=-(xy)^2*(x-2y)^2
=-2^2*(1/2)^2
=-(2*1/2)^2
=-1^2
=-1