[tex]P=20 \ W \\ U=24 \ V \\ \boxed{R-?} \\ \boxed{I-?} \\ \bold{Rezolvare:} \\ \boxed{P=U \cdot I} \ \ \ \ \ \ \ \boxed{I=\frac{U}{R}} \Rightarrow U=I \cdot R\\ \Rightarrow P=I \cdot R \cdot I=R \cdot I^2 \\ I=\frac{P}{U}=\frac{20 \ W}{24 \ V} \\ \Rightarrow \boxed{I=0,833 \ A=\bold{833,3 \ mA}} \\ R=\frac{P}{I^2}=\frac{20 \ W}{(0,833 \ A)^2}=\frac{20 \ W}{0,694 \ A^2} \\ \Rightarrow \boxed{R=28,8 \ \Omega}[/tex]
