`a)`
Ta có : `2=sqrt4`
Vì : `3<4 to sqrt3<sqrt4`
hay `sqrt3<2`
`b)`
Ta có : `2sqrt5=sqrt(2^2 . 5)=sqrt20`
Vì : `20>19 to sqrt20>sqrt19`
hay `2sqrt5>sqrt19`
`c)`
Ta có :
`3sqrt5=sqrt(3^2 . 5)=sqrt45`
`5sqrt3=sqrt(5^2 . 3)=sqrt75`
Vì : `45<75 to sqrt45<sqrt75`
hay `3sqrt5<5sqrt3`
`d)`
Ta có : `2sqrt3=sqrt3+sqrt3`
`2+sqrt3=sqrt4+sqrt3`
Vì : `3<4 to sqrt3<sqrt4`
`to sqrt3+sqrt3<sqrt3+sqrt4`
hay `2sqrt3<2+sqrt3`
