\(a,=\sqrt{\dfrac{81}{25}}=\dfrac{9}{5}\\ b,\approx6,39\\ c,=\sqrt{8,1\cdot20\cdot8}=\sqrt{81\cdot16}=\sqrt{81}\cdot\sqrt{16}=9\cdot4=36\\ d,=\sqrt{\left(\sqrt{6}+\sqrt{5}\right)^2}-\sqrt{\left(\sqrt{6}-\sqrt{5}\right)^2}\\ =\sqrt{6}+\sqrt{5}-\sqrt{6}+\sqrt{5}=2\sqrt{5}\)
a) \(\sqrt{3\dfrac{6}{25}}=\sqrt{\dfrac{81}{25}}=\dfrac{9}{5}\)
b) \(\sqrt[3]{216}=6\)
c) \(\sqrt{8,1}.\sqrt{20}.\sqrt{8}=\dfrac{9\sqrt{10}}{10}.2\sqrt{5}.2\sqrt{2}=36\)
d) \(\sqrt{11+2\sqrt{30}}-\sqrt{11-2\sqrt{30}}=\sqrt{\left(\sqrt{6}+\sqrt{5}\right)^2}-\sqrt{\left(\sqrt{6}-\sqrt{5}\right)^2}=\sqrt{6}+\sqrt{5}-\sqrt{6}+\sqrt{5}=2\sqrt{5}\)
