Question

If V = 12R / (r + R) , then R =

Answer 1

Vr+vR=12R
vr=12R-vR
vr=R(12-v)
R=vr/12-v

Answer 2

$V=\frac{12R}{r+R}\\\\V(r+R)=12R\\\\Vr+VR=12R\\\\VR-12R=-Vr\\\\(V-12)R=-Vr\ \ \ \ /:(V-12)\neq0\\\\R=\frac{-Vr}{V-12}\\\\R=\frac{Vr}{12-V}$