= - - +B X6 1 1X X X X+ +3 36 1 1X= - - +( )3 3+ +X XX X( )- - +...

Bài 5.= - - +B x6 1 1x x x x+ +3 3x

( )

x x- - + +6 3x x x= +3- - - += -9+

( )( )

- +Vậy B x 3b) 2 3 2=- Û - =-3 2Û - =-Û =1x TmVậy x=1thì B=- 2