U2=R2*U/R1+R2 wie nach R1 umstellen

$${\mathtt{U2}} = {\frac{{\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{U}}}{{\mathtt{R1}}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{R2}}$$

$${\mathtt{U2}}{\mathtt{\,\times\,}}{\mathtt{R1}} = {\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{U}}{\mathtt{\,\small\textbf+\,}}{\mathtt{R2}}{\mathtt{\,\times\,}}{\mathtt{R1}}$$

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 !

Das war sicher so gemeint. Man kann im Nenner von einer Spannung keinen Widerstand subtrahieren.

U2=R2*U/(R1+R2)

Gruß Omi67