b-a/a²-b²=-(a-b)/(a+b)(a-b)=-1/a+b-n/mp²÷n³/m²p=-n/mp²×m²p/n³=-m²pn/mp²n³=-m/pn²1/x-1/x+1= 1/x-1*1/x+1=1/(x+1)(x-1)=1/x²-1 （这题是这...做好了不过谢谢