9/(a-3)+a²/(3-a)
=9/(a-3)-a²/(a-3)
=-(a²-9)/(a-3)
=-[(a+3)(a-3)]/(a-3)
=-(a+3)
=-a-3

明白请采纳,有疑问请追问!
有新问题请求助,谢谢!