`C=\frac{x+2}{\sqrt{x}}` ĐKXĐ: `x>0` Ta có: `C-1/4` `=\frac{x+2}{\sqrt{x}}-1/4` `=\frac{4(x+2)-\sqrt{x}}{4\sqrt{x}}` `=\frac{4x-\sqrt{x}+8}{4\sqrt{x}}` Ta lại có:`4x-\sqrt{x}+8` `=4x-\sqrt{x}+1/16+127/16` `=(2\sqrt{x}-1/4)^2+127/16` Mà
`(2\sqrt{x}-1/4)^2≥0∀x>0<=>(2\sqrt{x}-1/4)^2+127/16≥127/16>0∀x>0` Và `4\sqrt{x}>0∀x>0` `=>C-1/4>0<=>C>1/4`
