VD1

a)

`A=sqrtx+5`

có `sqrtx>=0=>sqrtx+5>=5`

DBXR khi `sqrtx=0=>x=0`

`=>A_("min")=5` khi `x=0`

b)

`B=2sqrtx+3`

có `sqrtx>=0=>2sqrtx>=0=>2sqrtx+3>=3`

DBXR khi `sqrtx=0=>x=0`

`=>B_("min")=3` khi `x=0`

c)

`C=3sqrtx-1`

`sqrtx>=0=>3sqrtx>=0=>3sqrtx-1>=-1`

DBXR khi `sqrtx=0=>x=0`

`=>C_("min")=-1` khi `x=0`

VD2

a)

`D=-sqrtx+12`

`sqrtx>=0=>-sqrtx<=0=>-sqrtx+12<=12`

DBXR khi `sqrtx=0=>x=0`

`=>D_("max")=12` khi `x=0`

b)

`E=-2sqrtx+9`

`sqrtx>=0=>-sqrtx<=0=>-2sqrtx<=0=>-2sqrtx+9<=9`

DBXR khi `sqrtx=0=>x=0`

`=>E_("max")=9` khi `x=0`

c)

`F=-3sqrtx-2022`

`sqrtx>=0=>-3sqrtx<=0=>-3sqrtx-2022<=-2022`

DBXR khi `sqrtx=0=>x=0`

`=>F_("max")=-2022` khi `x=0`