判断下列级数的敛散性最好能有解题过程.重点是（6）.还有几题，一定有回报！

作为准备工作,先列几个基本极限.①lim{x → 0} ln(1+x)/x = 1.②lim{x → 0} (a^x-1)/x = ln(a) (a > 0).③lim{x → 0} (1-cos(x))/x² = 1/2.④lim{x → 0} arctan(x)/x = 1.⑤lim{x → +∞} ln(x)/x^α = 0 (...