Em cần hỗ trợ câu nào em ơi?
`a, A= 6 sqrt 27 - 2 sqrt 75 - 1/2 sqrt 300`
`= 6 sqrt(9.3) - 2 sqrt(25.3) - 1/2sqrt(100.3)`.
`= 18sqrt3 - 10sqrt3 - 5 sqrt 3`.
`= 3 sqrt 3`.
`b, B = 2 sqrt 125 + sqrt((1-sqrt5)^2) - 4/(sqrt5+1)`.
`= 10 sqrt 5 + sqrt 5 - 1 - ((sqrt5+1)(sqrt5-1))/(sqrt5+1)`
`= 10 sqrt 5 + sqrt 5 - 1 - sqrt 5 + 1`
`= 10 sqrt 5`.
`c, C = 2/(sqrt3+1) - 1/(sqrt3-2) + 12/(sqrt3+3)`
`= ((sqrt3+1)(sqrt3-1))/(sqrt3+1) + ((sqrt3-2)(sqrt3+2))/(sqrt3-2) + (2.(sqrt3+3)(3-sqrt3))/(sqrt3+3)`
`= sqrt 3 - 1 + sqrt 3 + 2(3 - sqrt 3)`
`= 2 sqrt 3 - 1 + 6 -6sqrt3`
`= 5 - 4 sqrt 3`.
`D = sqrt 5 - sqrt(13-4sqrt(9-4 sqrt 5))`
`= sqrt 5 - sqrt(13 - 4(sqrt5-2))`
`= sqrt 5 - sqrt(21 - 4sqrt5)`
`= sqrt 5 - sqrt(20 - 4 sqrt 5 + 1)`
`= sqrt 5 - sqrt((sqrt 20 - 1)^2)`
`= sqrt 5 - sqrt 20 + 1`
`= - sqrt 5 + 1`.
