$a)d=a\sqrt{2}=7\text{cm}\cdot \sqrt{2}=7\sqrt{2}\text{cm}$  

$b)d=8,5\text{cm}\cdot \sqrt{2}=8,5\sqrt{2}\text{cm}$  

$c)d=2\sqrt{2}\text{cm}\cdot \sqrt{2}=2\sqrt{4}\text{cm}=2\cdot 2\text{cm}=4\text{cm}$  

$d)d=\sqrt{800}\text{m}\cdot \sqrt{2}=\sqrt{1600}\text{m}=40\text{m}$  

$e)e=\sqrt{6}\text{cm}\cdot \sqrt{2}=\sqrt{12}\text{cm}=\sqrt{3\cdot 4}\text{cm}=\sqrt{3}\cdot \sqrt{4}\text{cm}=\sqrt{3}\cdot 2\text{cm}=2\sqrt{3}\text{cm}$  

$f)f=\frac{\sqrt{2}}{2}\text{cm}\cdot \sqrt{2}=\frac{\sqrt{4}}{2}\text{cm}=\frac{2}{2}\text{cm}=1\text{cm}$