题目应是：已知 a-2b=-½ ab=2 求-a⁴b²+4a³b³-4a²b⁴-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