Question

[Ling ling 2k7]

1) cho B= \(\dfrac{1-5\sqrt{x}}{x-1}\)

Tìm x thuộc R để B nguyên

2) Tính 

+ \(\sqrt{8-2\sqrt{15}}.\left(\sqrt{60}+6\right):2\sqrt{3}\)

+ \(\sqrt{5-\sqrt{21}}-\sqrt{\dfrac{7}{2}}\)

Answer 1

[Nguyễn Lê Phước Thịnh]

Bài 2: 

a: Ta có: \(\sqrt{8-2\sqrt{15}}\cdot\left(\sqrt{60}+6\right):2\sqrt{3}\)

\(=\left(\sqrt{5}-\sqrt{3}\right)\cdot\sqrt{12}\left(\sqrt{5}+\sqrt{3}\right):2\sqrt{3}\)

\(=2\sqrt{12}:2\sqrt{3}\)

=2

b: Ta có: \(\sqrt{5-\sqrt{21}}-\sqrt{\dfrac{7}{2}}\)

\(=\dfrac{\sqrt{10-2\sqrt{21}}-\sqrt{7}}{\sqrt{2}}\)

\(=\dfrac{\sqrt{7}-\sqrt{3}-\sqrt{7}}{\sqrt{2}}\)

\(=-\dfrac{\sqrt{6}}{2}\)