a²-4/4-2a=(a+2)(a-2)/-2(a-2)=-(a+2)/2x/x²-1 + 3x+1/x²-1 +2x+3/ 1-x² =x/x²-1 + 3x+1/x²-1 -（2x+3）/x²-1 =(x+3x+1-2x-3)/(x²-1）=(2x-2)/(x²-1)=2(x-1)/(x+1)(x-...