Đáp án+Giải thích các bước giải:
`a)A=4x-\sqrt{x}+1(x>=0)`
`A=4x-2*2\sqrt{x}*1/4+1/16+15/16`
`A=(2\sqrt{x}-1/4)^2+15/16`
Vì `(2\sqrt{x}-1/4)^2>=0`
`=>(2\sqrt{x}-1/4)^2+15/16>=15/16`
`=>A>=15/16`
Dấu "=" xảy ra khi `2\sqrt{x}=1/4<=>x=1/64`
`b)B=3x-3\sqrt{x}+5(x>=0)`
`B=3(x-\sqrt{x}+1/4)-3/4+5`
`B=3(\sqrt{x}-1/2)^2+17/4`
Vì `3(\sqrt{x}-1/2)^2>=0`
`=>3(\sqrt{x}-1/2)^2+17/4>=17/4`
`=>B>=17/4`
Dấu "=" xảy ra khi `\sqrt{x}=1/2<=>x=1/4`
`c)C=5x+2\sqrt{x}-1(x>=0)`
Vì `x>=0`
`=>5x>=0`
`x>=0=>2\sqrt{x}>=0`
`=>5x+2\sqrt{x}>=0`
`=>C>=-1`
Dấu "=" xảy ra khi `x=0.`
