giúp e với ạaaaaa....

`a,A=5\sqrt{2}-\sqrt{18}`

`A=5\sqrt{2}-3\sqrt{2}`

`A=2\sqrt{2}`

`b,B=\sqrt{45}+\sqrt{20}-\sqrt{5}`

`B=3\sqrt{5}+2\sqrt{5}-\sqrt{5}`

`B=4\sqrt{5}`

`c,C=3/2 \sqrt{20}-\sqrt{80}-2\sqrt{5}`

`C=3/2 .2\sqrt{5}-4\sqrt{5}-2\sqrt{5}`

`C=3\sqrt{5}-4\sqrt{5}-2\sqrt{5}`

`C=-3\sqrt{5}`

Bài 3:

`a,A=(\sqrt{2}-1). (2+\sqrt{2})/(2\sqrt{2})`

`A=(\sqrt{2}-1). [(\sqrt{2}+1).\sqrt{2})/(2\sqrt{2}]`

`A=(\sqrt{2}-1). (\sqrt{2}+1)/(2)`

`A=(2-1)/(2)`

`A=1/2`

`b,B=( (3-\sqrt{3})/(\sqrt{3}-1)+1 )(\sqrt{3}-1)`

`B=[ (\sqrt{3}(\sqrt{3}-1))/(\sqrt{3}-1)+1 ](\sqrt{3}-1)`

`B=( \sqrt{3}+1 )(\sqrt{3}-1)`

`B=3-1=2`