一个点到两个定点的距离乘积为定值，这个点的轨迹是什么？ 第1页

                {         a         ,         b         }         =         {         Sqrt         [(         x         +         1         )         ^         2         +         y         ^         2         ],         Sqrt         [(         x         -1         )         ^         2         +         y         ^         2         ]};                            plot2d         =         ContourPlot         [         #         ,{         x         ,         -3         ,         3         },{         y         ,         -3         ,         3         },         Contours         ->         {         Automatic         ,         25         },         ColorFunction         ->         "LightTemperatureMap"         ,         Frame         ->         False         ,         ImageSize         ->         360         ]         &         ;                            plot3d         =         Plot3D         [         First         [         z         /.         Solve         [         #         ==         z         ,         z         ]],{         x         ,         -3         ,         3         },{         y         ,         -3         ,         3         },         AspectRatio         ->         1         ,         BoxRatios         ->         1         ,         ViewVertical         ->         {         0.132         ,         0.365         ,         0.922         },         ViewPoint         ->         {         -1.06         ,         -2.93         ,         1.32         },         ColorFunction         ->         "TemperatureMap"         ,         Axes         ->         False         ,         ImageSize         ->         360         ]         &         ;                            show         =         Row         @         {         plot3d         [         #         ],         plot2d         [         #         ]}         &         ;