.Bài 1:Cho $U=U_{1}+(\frac{U_{1}}{R}+\frac{U_{1}}{R_{v}})$(2R+3R). C/m $6U_{1}+5U_{1}.\frac{R}{R_{v}}$ Bài 2:Cho $U=U_2+(\frac{U_2}{2R}$+$\frac{U_2}{R_v})(2R+3R)$. C/m $U=3U_2+4U_2.$$\frac{R}{Rv}$
Bài 3:Cho $U=U3+($$\frac{U3}{3R}+\frac{U3}{Rv}$$)(R+2R)$. Cm $U=2U3+U3.$$\frac{R}{Rv}$