`a)` Xem lại đề `?`
`b) 23sqrt{9x - 9} - 14sqrt{16x - 16} + 27sqrt{(x - 1)/(81)} = 12`
`<=> 23.3sqrt{x - 1} - 14.4.sqrt{x - 1} + 27.(1)/(9).sqrt{x - 1} = 12`
`<=> 16sqrt{x - 1} = 12`
`<=> sqrt{x - 1} = 3/4`
`=> x - 1 = 9/16`
`<=> x = 25/16`
`c) sqrt{18x + 9} - sqrt{8x + 4} + 1/(3)sqrt{2x + 1} = 4`
`<=> 3sqrt{2x + 1} - 2sqrt{2x + 1} + 1/(3)sqrt{2x + 1} = 4`
`<=> 4/(3)sqrt{2x + 1} = 4`
`<=> sqrt{2x + 1} = 3`
`=> 2x + 1 = 9`
`<=> x = 4`