[tex]\Delta x=2,5i\\i=\frac{\lambda D}{2l}=>\frac{D}{2l}=\frac{i}{\lambda} \\ \delta=e(n-1)\\ \Delta x=\frac{D \delta}{2l} =\frac{\delta i}{\lambda}=\frac{e(n-1)i}{\lambda}=>n-1=\frac{\lambda \Delta x}{ei}=>n=\frac{\lambda \Delta x}{ei}+1=\frac{0,7*2,5i}{1,4i}+1= 1,25+1=2,25=>n=2,25[/tex]