（2a-b)零次方≠1 (本题改一下,否则不好做)所以2a=ba²-3ab+2b²分之a²+2ab-b²=(a²+2ab-b²)/(a²-3ab+2b²)=(a²+4a²-4a²)/(a²-6a²+8a²)=a²...