30%=30/100=0,3
30% числа x это 0,3x
[m]0,3x=\frac{3}{\sqrt{7-\sqrt{40}}}+\frac{3}{\sqrt{5}+\sqrt{2}}[/m]
[m](\sqrt{5}+\sqrt{2})^2=5-2\sqrt{10}+2[/m]
Значит, можно заметить, что
[m]7-\sqrt{40}=5-2\sqrt{10}+2=(\sqrt{5}-\sqrt{2})^2[/m]
[m]\sqrt{7-\sqrt{40}}=\sqrt{(\sqrt{5}-\sqrt{2})^2}=\sqrt{5}-\sqrt{2}[/m]
[m]x=\frac{10}{3}\cdot (\frac{3}{\sqrt{5}-\sqrt{2}}+\frac{3}{\sqrt{5}+\sqrt{2}})[/m]
[m]x=\frac{1}{10}\cdot \frac{\sqrt{5}+\sqrt{2}+\sqrt{5}-\sqrt{2}}{(\sqrt{5}-\sqrt{2})(\sqrt{5}+\sqrt{2})}[/m]
[m]x=\frac{1}{10}\cdot \frac{2\sqrt{5}}{(\sqrt{5})^2-(\sqrt{2})^2}[/m]
[m]x=\frac{2\sqrt{5}}{30}[/m]