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A.m＜n                        B.m＞n                        C.m＝n                        D.不能確定

A.|x+y|＜|1+xy|                                                 B.|x+y|=|1+xy|

C.|x+y|＞|1+xy|                                                 D.|x+y|≥|1+xy|

A.                                                B.≤

C.                                                D.≥

A.                      B.

C.≥                     D.

A.a＞c                                                            B.a=c

C.a＜c                                                            D.a、c大小不確定

A.a＞b＞c                    B.b＞c＞a                    C.c＞a＞b                    D.a＞c＞b

A.＜－1                                                B.＞－1

C.≤－1                                                D.≥－1

求證：(1)c²＞ab；(2)c－＜a＜c+.