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A.若直線(xiàn)l₁與l₂都無(wú)斜率，則l₁與l₂一定不垂直

B.兩直線(xiàn)l₁與l₂中一條無(wú)斜率，另一條斜率為0，則有l₁⊥l₂

C.兩條直線(xiàn)l₁與l₂都有非零的斜率，且k₁·k₂=－1，則l₁⊥l₂

D.若l₁⊥l₂，則k₁·k₂=－1

A.平行                                                            B.垂直

C.相交但不垂直                                                D.以上都不對(duì)

A.B=－3                                                         B.B=3

C.B=－1                                                         D.B=1

A.α₁－α₂＝90°                                     B.α₂－α₁＝90°

C.|α₁－α₂|＝90°                                  D.α₁＋α₂＝180°

A.平行                                                          B.垂直

C.相交但不垂直                                              D.與n的值有關(guān)