~ Bạn tham khảo ~
`(6)/(1-\sqrt(3))-(2\sqrt(3))/(2+\sqrt(3))`
`=(6(2+\sqrt3))/((1-\sqrt(3))(2+\sqrt3))-(2\sqrt(3)(1-\sqrt(3)))/((1-\sqrt(3))(2+\sqrt3))`
`=(12+6\sqrt3)/(-1-\sqrt3)-(2\sqrt(3)-6)/(-1-\sqrt3)`
`=(12+6\sqrt3-2\sqrt(3)+6)/(-1-\sqrt3)`
`=(18+4\sqrt3)/(-1-\sqrt3)`
`= 3-7\sqrt3`