Đáp án+Giải thích các bước giải:
`a)\sqrt{8-2\sqrt{15}}-\sqrt{80}+\frac{10}{\sqrt{5}}-(\sqrt{5}-2).\sqrt{5}`
`=\sqrt{(\sqrt{5}-\sqrt{3})^2}-4\sqrt{5}+\frac{2\sqrt{5}.\sqrt{5}}{\sqrt{5}}-5+2\sqrt{5}`
`=|\sqrt{5}-\sqrt{3}|-2\sqrt{5}-5+2\sqrt{5}`
`=\sqrt{5}-\sqrt{3}-5`
`b)\frac{4}{\sqrt{3}+1}-\frac{5}{\sqrt{3}-2}+\frac{3\sqrt{3}-3}{\sqrt{3}-3}`
`=\frac{4(\sqrt{3}-1)}{3-1}-\frac{5(\sqrt{3}+2)}{3-4}+\frac{\sqrt{3}(3-\sqrt{3})}{\sqrt{3}-3]`
`=\frac{4(\sqrt{3}-1)}{2}-\frac{5(\sqrt{3}+2)}{-1}-\sqrt{3}`
`=2(\sqrt{3}-1)+5(\sqrt{3}+2)-\sqrt{3}`
`=2\sqrt{3}-2+5\sqrt{3}+10-\sqrt{3}`
`=6\sqrt{3}+8`
Bài `2:`
`a)\sqrt{9-x^2}=2(-3<=x<=3)`
`<=>9-x^2=4`
`<=>x^2=5`
`<=>x=+-\sqrt{5}(tm)`
Vậy `S={+-\sqrt{5}}`
`b)\sqrt{2x^2-4x+9}=3+x(x>=-3)`
`<=>2x^2-4x+9=9+6x+x^2`
`<=>2x^2-x^2-4x-6x+9-9=0`
`<=>x^2-10x=0`
`<=>x(x-10)=0`
`<=>[(x=0),(x=10):}(tm)`
Vậy `S={0;10}`
