给下列词语分类。盛气凌人同心协力漫不经心高瞻远瞩神机妙算聚精会神贬义词：褒义词：

Question

给下列词语分类。  
盛气凌人    同心协力    漫不经心 
高瞻远瞩    神机妙算    聚精会神
贬义词：                                                                                                  
褒义词：                                                                                                 

Answer 1

((3)/(a+1)−(a−3)/(a2−1))÷(a)/(a−1)
=(3(a−1)−a+3)/((a+1)(a−1))×(a−1)/(a)
=(2)/(a+1)．
∵tan45°＞a＞sin30°，
∴1＞a＞(1)/(2)，
当a=0.75时，原式=(8)/(7)．