1.化简[（bc-a^2）/ab]+[(ac-b^2)/bc]+[（ab-c^2)/ac]

1 =(bc^2-a^2c+a^2c-ab^2+ab^2-bc^2)/abc=0
2 (a+1)(a-1)/(a-2)(a-3)÷[x/(x+2)(x-2) 都是x?2..[(a^2-1)/a^2-5a+6]÷[(a^2+a-2)/a-3]-[(a+3)/(a^2-4)]2 =(a+1)(a-1)/(a-2)(a-3) X (a-3)/((a+2)(a-1) -(a+3)/(a+2)(a-2) =(a+1)/(a+2)(a-2) - (a+3)/(a+2)(a-2)=-2/(a+2)(a-2)=2/(4-a^2)