1.解:(1)11330nnnnSnnSnSSn12121121411nnnnnnSSSSnnSSSSnn...
301.已知数列1,1naa,前n项和nS满足130nnnSnS(1)求na的通项公式(2)设2nnnnca,若数列nc...
1.思路:从所给条件入手,进行不等式化简:1bcacab222babcacacabbcabc,观察到余弦定理公...
191.△ABC各角的对应边分别为cba,,,满足1bcacab,则角A的范围是A.(0,]3B.(0,]6C.[,)3D.[,)62.在ABC中,角,,A...