题目内容：

计算：看的懂的来~字母后面的2是平方的意思~
(1/9a2+6a+1 - 1/3a+1) / a2/3a2+a

优质解答

[1/(9a²+6a+1)-1/(3a+1)] / [a²/(3a²+a)]
=[1/(3a+1)²- 1/(3a+1)] / [a/(3a+1)]
=[1/(3a+1)- 1] / a
=[(1-3a-1)/(3a+1)]/a
=-3/(3a+1)