`1)\sqrt{2x-5}-2\sqrt{3}=0`
`<=>{(2x-5>=0),(\sqrt{2x-5}=2\sqrt{3}):}`
`<=>{(2x>=5),(2x-5=4.3):}`
`<=>{(x>=5/2),(2x=12+5):}`
`<=>{(x>=5/2),(x=17/2(tm)):}`
Vậy `S={17/2}`
`2)\sqrt{4x-20}+6\sqrt{\frac{x-5}{9}}-1/3\sqrt{9x-45}=6(x>=5)`
`<=>2\sqrt{x-5}+6.1/3.\sqrt{x-5}-1/3 .3.\sqrt{x-5}=6`
`<=>2\sqrt{x-5}+2\sqrt{x-5}-\sqrt{x-5}=6`
`<=>3\sqrt{x-5}=6`
`<=>\sqrt{x-5}=2`
`<=>x-5=4`
`<=>x=9(tm)`
Vậy `S={9}`
`3)\sqrt{4x^2-9}=2\sqrt{2x+3}(x>=-3/2)`
`<=>4x^2-9=4(2x+3)`
`<=>4x^2-9=8x+12`
`<=>4x^2-8x-21=0`
`<=>4x^2+6x-14x-21=0`
`<=>2x(2x+3)-7(2x+3)=0`
`<=>(2x+3)(2x-7)=0`
`<=>2x+3=0` hoặc `2x-7=0`
`<=>x=-3/2(tm)` hoặc `x=7/2(tm)`
Vậy `S={-3/2;7/2}`