Đáp án:
`a)P=-x+4sqrtx-1(x>=0)`
`P=-x+4sqrtx-4+3`
`P=-(x-4sqrtx+4)+3`
`P=-(sqrtx-2)^2+3<=3`
Dấu "=" xảy ra khi `sqrtx=2<=>x=4.`
`b)P=10/(2x+sqrtx+2)(x>=0)`
Vì `x>=0=>{(2x>=0),(sqrtx>=0):}`
`=>2x+sqrtx+2>=2>0`
`=>10/(2x+sqrtx+2)<=10/2=5`
`=>P<=5`
Dấu "=" xảy ra khi `x=0`.
`c)P=-x-6sqrtx+3`
Vì `x>=0=>{(-x<=0),(-6sqrtx<=0):}`
`=>P<=3`
Dấu "=" xảy ra khi `x=0.`
`d)P=\sqrt{6-2\sqrtx-x}`
`x>=0=>-x-2sqrtx<0`
`=>6-2sqrtx-x<=6`
`=>P<=sqrt6`
Dấu "=" xảy ra khi `x=0`
