计算：1/(x-2)+2/(x+1)-2/(x-1) -1/(x+2)1/(x-2)+2/(x+1)-2/(x-1) -1/(x+2)=1/(x-2)-1/(x+2)+2/(x+1)-2/(x-1)=4/(x²-4)-2/(x²-1)=(2x²+4)/(x²-4)(x²-1)