2/a-1 - a+2/a²+8a-9 / 3/2a+18
问题描述：
2/a-1 - a+2/a²+8a-9 / 3/2a+18
答
2/(a-1) -( a+2)/(a²+8a-9) / 3/2a+18
=2/(a-1) - (a+2)/(a+9)(a-1)×2（a+9）/3
=2/(a-1) - (a+2)/(a-1)×2/3
=(-2a+2)/(a-1)/3
=-2/3(a+2)/(a+9)(a-1)×2这步怎么做的慢慢看一看啊