因为arctanx＋arccotx＝π/2,所以x≠0时,arctanx＋arctan(1/x)＝π/2,所以arctan(n^2+1)＋arctan(n^2+2)＋……＋arctan(n^2+n)－nπ/2＝－arctan[1/(n^2+1)]－arctan[1/(n^2+2)]－……－arctan[1/(n^2+n)]arctanx在[...