证明：K/(K+1)+1/[(K+1)(K+2)] =[K(K+2)+1]/[(K+1)(K+2)] （注：通分,公分母 为[(K+1)(K+2)]） =（K+2K+1）/[(K+1)(K+2)] =(K+1)/[(K+1)(K+2)] （注：分子分母同时约分,约去(K+1) ） =(K+1)/(K+2) 即 证明了....