变换为(n^(2/3)/[(n^2+n+7)^1/3])^(3*(1/3))
变换为(n^2)/[(n^2+n+7)]^(1/3)
变换为(1)/[(1+(1/n)+(7/n))]^(1/3)
变换为(1)/[(1+(0)+(0))]^(1/3)
1