空間坐標中            是兩兩互相垂直,且長度為1的向量,因此

                                            

                         而且

                                      

                          

                                 

                                         

                                         

                          由此可得                                 

                          

                          

                                                   

                          於是

                                                          

                          其實,      即點( x, y, z )與原點( 0, 0, 0 )的距離,由兩點間距離公式可知

                     .        

                           又若兩向量互相垂直,則其內積為零,即

                           

                           .

                          

                                        ,       ,

                                    .

　

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