R= [(n1-n2)/n1+n2)]2 also erst mal wurzel
√R = (n1-n2)/n1+n2 | -n2
-n2 + √R = (n1-n2)/n1 | *n1
(-n2 + √R)*n1 = n1 - n2 | - n1
(-n2 + √R)*n1 - n1 = - n2 | * -1
(n2 - √R)*n1 + n1 = n2 | n1 ausklammern
(n2 - √R + 1 )*n1 = n2 | :Klammer
n1 = n2 / ( n2 - √R + 1 )