Giúp Nguyễn Duy

  !  " #  " !! $   %&'() *   " !+#  " !  * ,-  " !"# " !,-! " ,-   CÐ CT x m x m = −   = +  ./'01234'5&67 89:&)(;  $< = $% ,,-> #"=> !",,-> " ,, " ",,--             CÐ CT CÐ CT x x m m m x x m m m  < <  − < + < < −  ⇔ ⇔    < < − < < + − < <     ?@4' 89:A/&34'),, " 