Giải thích các bước giải:
ĐKXĐ : `x>=-5`
`sqrt(4x+20)-2sqrt(x+5)+sqrt(9x+45)=6`
`<=> sqrt(4(x+5))-2sqrt(x+5)+sqrt(9(x+5))=6`
`<=> 2sqrt(x+5)-2sqrt(x+5)+3sqrt(x+5)=6`
`<=> 3sqrt(x+5)=6`
`<=> sqrt(x+5)=2`
`<=> x+5=4`
`<=> x=-1 \ \ text{(tmđk)}`
Vậy `S={-1}`