$${\mathtt{U2}} = {\frac{{\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{U}}}{{\mathtt{R1}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{R2}}$$
$${\mathtt{U2}}{\mathtt{\,\times\,}}{\mathtt{R1}} = {\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{U}}{\mathtt{\,\small\textbf+\,}}{\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{R1}}$$
U2*R1 - R2*R1 = R2*U
R1 *( U2-R2 ) = R2*U
$${\mathtt{R1}} = {\frac{{\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{U}}}{\left({\mathtt{U2}}{\mathtt{\,-\,}}{\mathtt{R2}}\right)}}$$
Gruß radix
!