Đáp án + Giải thích các bước giải:
Câu 2:
`a.`
`sqrt(x+5)=3`
`<=>x+5=3^2`
`<=>x=9-5=4`
Vậy `x=4`
`b. `
Ta có:
`(2sqrt6)^2=2^2.(sqrt6)^2=4.6=24`
`5^2=25`
Vì `25>24` nên `5>2sqrt6`
`c.`
`sqrt(12,1).sqrt40=sqrt\frac{121}{10}.sqrt(2^2. 10)=\frac{sqrt121}{sqrt10}.2sqrt10=11.2=22`
`sqrt(16.400)=sqrt16.sqrt400=4.20=80`
`d.`
`sqrt(11+4sqrt6)-sqrt(9-4sqrt2)`
`=sqrt(8+4sqrt6+3)-sqrt(8-4sqrt2+1)`
`=sqrt((2sqrt2+sqrt3)^2)-sqrt((2sqrt2-1)^2)`
`=|2sqrt2+sqrt3|-|2sqrt2-1|`
`=2sqrt2+sqrt3-2sqrt2+1`
`=sqrt3+1`
