`1) 5-3\sqrt{x}=6\sqrt{x}+7 (x\ge0)`
`<=> -3\sqrt{x}-6\sqrt{x}=7-5`
`<=> -9\sqrt{x}=2`(sai $\forall x$)
`=> x\in∅`
`2) 15-8\sqrt{x}=9-5\sqrt{x} (x\ge0)`
`<=> -8\sqrt{x}+5\sqrt{x}=9-15`
`<=> -3\sqrt{x}=-6`
`<=> \sqrt{x}=2`
`<=> x=4`
`3) 5-(\sqrt{x}-6)=4(3-2\sqrt{x}) (x\ge0)`
`<=> 5-\sqrt{x}+6=12-8\sqrt{x}`
`<=> -\sqrt{x}+8\sqrt{x}=12-5-6`
`<=> 7\sqrt{x}=1`
`<=> \sqrt{x}=1/7`
`<=> x=1/49`
`4) 7-(2\sqrt{x}+4)=-(\sqrt{x}+4) (x\ge0)`
`<=> 7-2\sqrt{x}-4=-\sqrt{x}-4`
`<=> 3-2\sqrt{x}=-\sqrt{x}-4`
`<=> -2\sqrt{x}+\sqrt{x}=-4-3`
`<=> -\sqrt{x}=-7`
`<=> \sqrt{x}=7`
`<=> x=49`
