题目先化简,再求值:(2aa2−1−1a+1)÷a+2a2−a\left(\dfrac{2a}{a^{2}-1}-\dfrac{1}{a+1}\right)\div \dfrac{a+2}{a^{2}-a}(a2−12a−a+11)÷a2−aa+2,其中a=5a=\sqrt {5}a=5.知识点：分式的化简求值章节：数与式 / 分式
