空間坐標系中,當

                                                                           

                                                      

                                                                  

                                                                   　

                     所以     

                                     

*                                  

                    也可說   ( x1, y1, z1)+( x2, y2, z2 ) = ( x1+ x2, y1+ y2, z1+ z2 ).

　

                   

　

　

　

                      仿照加法,我們可得到向量減法法則,即

                                               

                                            *

                                                或 ( x1, y1 , z1) - ( x2, y2, z2 ) = ( x1- x2, y1- y2, z1- z2 ).

                  

                      

　

　

　

              

                                                 

                                     所以

                                                 

　

　

                       

　

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