การคูณและหารที่มีเครื่องหมายกรณฑ์

ตัวอย่าง   จงหาร  +2      ด้วย    2+

                         - 1                       - 2                      

 

วิธีทำ     +2       2+           =       + 2   .    -  2

            - 1           - 2                - 1       2 +    

 

                                                        =         ( + 2 ) ( -  2)

                                                                              ( - 1)  ( 2 +)

                                                                   =       5 - 4

                                                       +3 - 2 -                

 

                                                    =          1

                                                                         + 1

                                                 

                                                    =          1         .    - 1 

                                                                         + 1         - 1

                                                                                                 

   =     -1 

                                                                      3 - 1       

  =    - 1 

                                                                        2