题目先化简(a2−1a−3−a−1)÷a+1a2−6a+9(\frac{{a}^{2}-1}{a-3}-a-1)÷\frac{a+1}{{a}^{2}-6a+9}(a−3a2−1−a−1)÷a2−6a+9a+1,然后从−1-1−1,000,111,333中选一个合适的数作为aaa的值代入求值.知识点：分式的化简求值章节：数与式 / 分式
