`a)M=({2x+1}/{\sqrt{x^3}-1}- {\sqrt{x}}/{x+\sqrt{x}+1})( {1+\sqrt{x^3}}/{1+\sqrt{x}} - \sqrt{x}) (x\ge0, x\ne9)`
`M=({2x+1}/{(x+\sqrt{x}+1)(\sqrt{x}-1)}- {\sqrt{x}(\sqrt{x}-1)}/{(x+\sqrt{x}+1)(\sqrt{x}-1)})( {(x-\sqrt{x}+1)(\sqrt{x}+1)}/{1+\sqrt{x}} - \sqrt{x}) `
`M= {2x+1-x+\sqrt{x}}/{(x+\sqrt{x}+1)(\sqrt{x}-1)}( x-\sqrt{x}+1 - \sqrt{x})`
`M= {x+\sqrt{x}+1}/{(x+\sqrt{x}+1)(\sqrt{x}-1)}( x-2\sqrt{x}+1)`
`M= {(x+\sqrt{x}+1)(\sqrt{x}-1)}/{(x+\sqrt{x}+1)}`
`M=\sqrt{x}-1.`
`b)M=3⇔\sqrt{x}-1=3`
`⇔\sqrt{x}=3+1=4`
`⇔(\sqrt{x})^2=4^2`
`⇒x=16`
Vậy `M=3⇔x=16.`
`c) M>0⇔\sqrt{x}-1>0`
`⇒\sqrt{x}>1`
`⇔\sqrt{x}>\sqrt{1}`
`⇒x>1`
Vậy `M>0⇔x>1.`
