题目先化简,再求值:(3a+1−a+1)÷a2−4a2+2a+1(\frac{3}{a+1}-a+1)÷\frac{{a}^{2}-4}{{a}^{2}+2a+1}(a+13−a+1)÷a2+2a+1a2−4,再从−2-2−2,−1-1−1,000,111,222中取一个数代入求值其中.知识点：分式的化简求值章节：数与式 / 分式
