rút gọn biêu thức sau
a) A=\(\dfrac{1}{2+\sqrt{3}}\) +\(\dfrac{\sqrt{2}}{\sqrt{6}}\)-\(\dfrac{2}{3+\sqrt{3}}\)
b) B=\(\dfrac{3+\sqrt{5}}{\sqrt{2}+\sqrt{3+\sqrt{5}}}\)+\(\dfrac{3-\sqrt{5}}{\sqrt{2}-\sqrt{3-\sqrt{5}}}\)
c) C=\(\dfrac{4}{\sqrt{5}-1}\)+\(\dfrac{3}{\sqrt{5}-2}\)+\(\dfrac{16}{\sqrt{5}-3}\)
d)D=\(\dfrac{\sqrt{2}+\sqrt{3}+\sqrt{6}+\sqrt{8}+4}{\sqrt{2}+\sqrt{3}+\sqrt{4}}\)
a: \(=2-\sqrt{3}+\dfrac{1}{3}\sqrt{3}-1+\dfrac{1}{3}\sqrt{3}\)
\(=-\dfrac{1}{3}\sqrt{3}+1\)
b: \(=\dfrac{\sqrt{2}\left(3+\sqrt{5}\right)}{2+\sqrt{5}+1}+\dfrac{\sqrt{2}\left(3-\sqrt{5}\right)}{2-\sqrt{5}+1}\)
\(=\dfrac{\sqrt{2}\left(3+\sqrt{5}\right)}{3+\sqrt{5}}+\dfrac{\sqrt{2}\left(3-\sqrt{5}\right)}{3-\sqrt{5}}=2\sqrt{2}\)
