giúp mình câu này với ạ, mình cảm ơn.

`color{red}{ThanDongToanLiHoa}`

Câu `1` :

`a)` 

`P =`  `(\sqrt{5}-2)` . `\frac{\sqrt{15} + \sqrt{12} }{\sqrt{3}`

`P =`  `(\sqrt{5}-2)` . `\frac{\sqrt{3} .\sqrt{5} + \sqrt{4} . \sqrt{3} }{\sqrt{3}`

`P =`   `(\sqrt{5}-2)` . `(\sqrt{5}+2)`

`P = 1`

`b)`

`A= (\frac{1}(\sqrt{x}+5) - \frac{1}(\sqrt{x}-5))` : `\frac{\sqrt{x}}(x-25)`   và  `x > 0` ; `x\ne25`  

`A= [\frac{\sqrt{x} - 5}{(\sqrt{x}-5)(\sqrt{x}+5)}` `-` `\frac{\sqrt{x} + 5}{(\sqrt{x}-5)(\sqrt{x}+5)}]` `:` `\frac{\sqrt{x}}{x-25}`

`A= [\frac{\sqrt{x} - 5 - ( \sqrt{x}+5) }{(\sqrt{x}-5)(\sqrt{x}+5)}]` . `\frac{(\sqrt{x} - 5) - ( \sqrt{x}+5) }{\sqrt{x}}`

`A= \frac{\sqrt{x} - 5 -  \sqrt{x}- 5) {(\sqrt{x}-5)(\sqrt{x}+5)}` . `\frac{(\sqrt{x} - 5) - ( \sqrt{x}+5) }{\sqrt{x}}`

`A= \frac{-10}{(\sqrt{x}-5)(\sqrt{x}+5)}` . `\frac{(\sqrt{x} - 5) - ( \sqrt{x}+5) }{\sqrt{x}}`

`A= \frac{-10}{\sqrt{x}`

`->` Vậy `A= \frac{-10}{\sqrt{x}` và `x > 0` ; `x\ne25`