a-2b=0.5,ab=2,则(a-2b)^2=a^2+4b^2-4ab=0.25所以a^2+4b^2=0.25+4ab=0.25+4*2=8.25-a^4b^2+4a^3b^3-4a^2b^4=-a^2b^2(a^2+4b^2)+4a^3b^3=-(ab)^2(a^2+4b^2)+4(ab)^3=-2^2*8.25+4*2^3=-1