计算：(1/9a^2+6a+1-1/3a+1)/a^2/3a^2+a
问题描述：
计算：(1/9a^2+6a+1-1/3a+1)/a^2/3a^2+a
答
=(1/(3a+1)^2-1/(3a+1))/(a^2/3a^2+a)
=(3a/(3a+1)^2)/(a^2/3a^2+a)
=(3a/(3a+1)^2)/(a/(3a+1))
=3/(3a+1)