解：?$(1)R_{ L }=\frac {U_{L }}{I_{ L }}=\frac {{ 4 }\ \mathrm {V}}{{ 0.5 }\ \mathrm {A}}={ 8 } \ \mathrm {Ω}$?
?$ (2)I_{ }=\frac {U_{ }}{R_{ }+R_{ L }}=\frac {{ 6 }\ \mathrm {V}}{{ 8 } \ \mathrm {Ω}+{ 8 } \ \mathrm {Ω}}={ 0.375}\ \mathrm {A}$?
?$ P_{1 }=I_{ }^2R_{ }=({ 0.375}\ \mathrm {A})^2×{ 8 } \ \mathrm {Ω}={ 1.125 }\ \mathrm {W} $?
?$ (3)P_滑=\frac {U^2R_滑}{(R_滑+R_L)^2}，$?
當?$\frac {U^2R_1}{(R_1+R_L)^2}=\frac {U^2R_2}{(R_2+R_L)^2}$?時，
可得?$R_1R_2=R_L^2=(8 \ \mathrm {Ω})^2=64 \mathrm \ \mathrm {Ω}^2$?
