1/ Căn 20 - 4 chia 5 - căn 5 2/ x + 1 - 2 căn x chia căn x - x

Đáp án:

Giải thích các bước giải:

`\color{red}{\text{Câu 1 :} (\sqrt{20}-4)/(5-\sqrt{5} )}`$\\$`=((\sqrt{20}-4)(5+\sqrt{5}))/((5-\sqrt{5})(5+\sqrt{5}))=(10\sqrt{5}+10-20-4\sqrt{5})/(20)`$\\$`=(6\sqrt{5}-10)/(20)=(2(3\sqrt{5}-5))/(20)\color{green}{=(3\sqrt{5}-5)/(10)}`$\\$`\color{red}{\text{Câu 2 :}(x+1-2\sqrt{x})/(\sqrt{x}-x)`$\\$`=((\sqrt{x}-1)^2)/(\sqrt{x}-x)=((1-\sqrt{x})^2)/(\sqrt{x}(1-\sqrt{x}))\color{green}{=(1-\sqrt{x})/(\sqrt{x})}`

1) `(\sqrt{20}-4)/(5-\sqrt{5})`

`=((\sqrt{20}-4)(5+\sqrt{5}))/((5-\sqrt{5})(5+\sqrt{5}))`

`=(10\sqrt{5}+10-20-4\sqrt{5})/(20)`

`=(6\sqrt{5}-10)/(20)`

`=(2(3\sqrt{5}-5))/(20)`

`=(3\sqrt{5}-5)/(10)`

2) `(x+1-2\sqrt{x})/(\sqrt{x}-x)`

`=((\sqrt{x}-1)^2)/(\sqrt{x}-x)`

`=((1-\sqrt{x})^2)/(\sqrt{x}(1-\sqrt{x}))`

`=(1-\sqrt{x})/(\sqrt{x})`