已知a-2b-1/2,ab=2,求-a^4b^2+4a^3b^3-4a^2b^4的值

已知a-2b-1/2,ab=2,求-a^4b^2+4a^3b^3-4a^2b^4的值
已知a-2b-1/2,ab=2,求-a^4b^2+4a^3b^3-4a^2b^4的值

已知a-2b-1/2,ab=2,求-a^4b^2+4a^3b^3-4a^2b^4的值
-a^4b^2+4a^3b^3-4a^2b^4
=-a^2b^2(a^2-4ab+4b^2)
=-(ab)^2(a-2b)^2
=-(2)^2(1/2)^2
=-4x1/4
=-1