Question 121026
given:

{{{I=E/(R+r)}}}

to do:......solve for {{{R}}}

{{{I=E/(R+r) }}}..........multiply both sides by {{{ (R+r) }}}


{{{I(R+r)=(R+r)(E/(R+r)) }}}..........simplify


{{{I(R+r)=cross((R+r))(E/cross((R+r))) }}}..........

{{{IR+ Ir =E}}}.......move {{{Ir}}} to the right


{{{IR =E - Ir}}}....divide both sides by {{{I}}}


{{{IR/I =E/I - Ir/I}}}....simplify


{{{cross(I)R/cross(I) =E/I - cross(I)r/cross(I)}}}....


{{{R =E/I - r}}}....