Hướng dẫn giải:
`1)` `A=sqrt5(sqrt5-3)+sqrt45`
`=sqrt5.sqrt5-sqrt5 .3+sqrt45`
`=sqrt(5^2)-3sqrt5+3\sqrt45`
`=5-3sqrt5+3sqrt5`
`=5+(-3sqrt5+3sqrt5)`
`=5`
`2)` `A=sqrt(75.5).sqrt((1-sqrt3)^2)`
`=sqrt225.|1-sqrt3|`
`=sqrt(15^2).|1-sqrt3|`
`=15|1-sqrt3|`
`=15(sqrt3-1)` `(` do `1<sqrt3` `)`
`=15.sqrt3-15`
`=15sqrt3-15`
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Giải thích:
`@|A|={(A \text( khi ) A>=0),(-A \text( khi ) A<0):}`