Từ đồ thị: \(\frac{U_{L}^{\max }}{{{U}_{L1}}}=\frac{U_{L}^{\max }}{{{U}_{L2}}}=\frac{7}{4},\) và \(U_{L}^{\max }=\frac{U}{\sqrt{1-{{n}^{-2}}}}\xrightarrow{\frac{U_{L}^{\max }}{U}=\frac{14}{6}=\frac{7}{3}}\Rightarrow n=\frac{7\sqrt{10}}{20}\Rightarrow {{\cos }^{2}}{{\varphi }_{L}}=\frac{2}{1+n}=0,95.\)

 \({U_L} = L\omega .\frac{U}{R}\cos \varphi \Rightarrow \frac{1}{{{\omega ^2}}} = {\left( {\frac{U}{{{U_L}}}.\frac{L}{R}\cos \varphi } \right)^2} \Rightarrow \left\{ {\begin{array}{*{20}{c}} {\frac{1}{{\omega _1^2}} = {{\left( {\frac{U}{{{U_{L1}}}}.\frac{L}{R}\cos {\varphi _1}} \right)}^2}}\\ {\frac{1}{{\omega _2^2}} = {{\left( {\frac{U}{{{U_{L2}}}}.\frac{L}{R}\cos {\varphi _2}} \right)}^2}}\\ {\frac{1}{{\omega _L^2}} = {{\left( {\frac{U}{{U_L^{\max }}}.\frac{L}{R}\cos {\varphi _L}} \right)}^2}} \end{array}} \right.\)            (1).

Ta có:  \({P_1} = U{I_1}\cos {\varphi _1} = U\frac{U}{{{Z_1}}}\cos {\varphi _1} = \frac{{{U^2}}}{R}{\cos ^2}{\varphi _1}\)

 \({P_2} = U{I_2}\cos {\varphi _2} = U\frac{U}{{{Z_2}}}\cos {\varphi _2} = \frac{{{U^2}}}{R}{\cos ^2}{\varphi _2}.\)

       \(=>{{P}_{1}}+{{P}_{2}}=\frac{{{U}^{2}}}{R}({{\cos }^{2}}{{\varphi }_{1}}+{{\cos }^{2}}{{\varphi }_{2}})\xrightarrow{(2)}.\)       

Thế số: \({{P}_{1}}+{{P}_{2}}={{P}_{CH}}.2.{{\left( \frac{{{U}_{L}}}{U_{L}^{\max }} \right)}^{2}}{{\cos }^{2}}{{\varphi }_{L}}=287.2.{{\left( \frac{4}{7} \right)}^{2}}0,95=178,1\ W\)  . Chọn C.