a²+2a-b²-2b=a²+2a+1-b²-2b-1=（a+1）²-（b²+2b+1）=（a+1）²-（b+1）²=[a+1+b+1][a+1-(b+1)]=(a+b+2)(a-b)或者 a²+2a-b²-2b=a²-b²+2a-2b=(a+b)(a-b)+...