a²+b²+2a-4b+5=0a^2+2a+1+b^2-4b+4=0(a+1)^2+(b-2)^2=0则a+1=0b-2=0的a=-1,b=2则a²-2ab-3b²/a(a-b)+3ab+b²=(a²-2ab-3b²)/(a^2+2ab+b²)=(a²-2ab+b^2-4b²)/(a+b)^2...