I=E/(R+r)
P=RI²=>R=P/I²=P/[E²/(R+r)²]=P(R+r)²/E²=>RE²=P(R+r)²<=>RE²-PR²-Pr²-2PRr=0
-PR²+R(E²-2Pr)-Pr²=0
Δ=(E²-2Pr)²-4*P*Pr²=(12²-2*12*2)²-4*12*12*2=((144-48)²-1152=96²-1152=9216-1152=8064
R₁₂=(-E²+2Pr±√Δ)/(-2P)=(-144+48±√8064)/(-24)=(-96±90)/(-24)
R₁=(-96+90)/(-24)=6/24 Ω
R₂=(-96-90)/(-24)=186/24≅8 Ω