(x-3)/(x^2-1)÷(x^2-2x-3)/(x^2+2x+1)+1/(x-1)
=(x-3)/(x^2-1)*(x^2+2x+1)/(x^2-2x-3)+1/(x-1)
=(x-3)/(x-1)(x+1)*(x+1)^2/(x-3)(x+1)+1/(x-1)
=(x-3)/(x-1)*(x+1)/(x-3)(x+1)+1/(x-1)
=1/(x-1)+1/(x-1)
=2/(x-1)
=2/(-2-1)
=-2/3（2）某市建筑公司承建该市一段轻轨工程。为使工程能提前3个月完成，需将原来工作效率提高12.5%，问计划完成这 项任务需要几个月。。。。。。。。。。。过程