Question

1) Tính:

a) \(\sqrt{4.36}\)

b) (\(\sqrt{8}\) - 3\(\sqrt{2}\)) . \(\sqrt{2}\)

c)\(\dfrac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}\)

d) \(\dfrac{2}{\sqrt{5}+2}\) + \(\dfrac{2}{\sqrt{5}-2}\)

 

Answer 1

a: \(\sqrt{4\cdot36}=\sqrt{144}=12\)

b: \(\left(\sqrt{8}-3\sqrt{2}\right)\cdot\sqrt{2}\)

\(=\left(2\sqrt{2}-3\sqrt{2}\right)\cdot\sqrt{2}\)

\(=-\sqrt{2}\cdot\sqrt{2}=-2\)

c: \(\dfrac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}=\dfrac{-\sqrt{7}\left(1-\sqrt{2}\right)}{1-\sqrt{2}}=-\sqrt{7}\)

d: \(\dfrac{2}{\sqrt{5}+2}+\dfrac{2}{\sqrt{5}-2}\)

\(=\dfrac{2\left(\sqrt{5}-2\right)+2\left(\sqrt{5}+2\right)}{5-4}\)

\(=2\sqrt{5}-4+2\sqrt{5}+4=4\sqrt{5}\)