Question

gấp giúp mình với ạ

 

Answer 1

\(3\sqrt{20}+\sqrt{80}-\dfrac{1}{7}\sqrt{245}-5\sqrt{125}=3.\sqrt{2^2.5}+\sqrt{4^2.5}-\dfrac{1}{7}\sqrt{7^2.5}-5\sqrt{5^2.5}\)

\(=6\sqrt{5}+4\sqrt{5}-\sqrt{5}-25\sqrt{5}\)

\(=-16\sqrt{5}\)

\(\sqrt{32-10\sqrt{7}}+\dfrac{6}{\sqrt{7}-1}=\sqrt{\left(5-\sqrt{7}\right)^2}+\dfrac{6\left(\sqrt{7}+1\right)}{\left(\sqrt{7}+1\right)\left(\sqrt{7}-1\right)}\)

\(=\left|5-\sqrt{7}\right|+\dfrac{6\left(\sqrt{7}+1\right)}{6}=5-\sqrt{7}+\sqrt{7}+1=6\)