a)Rz=R1+R2+R3+R4
c)R12=R1+R2
R34=R3+R4
[tex]\frac{1}{Rz} =\frac{1}{R12}+\frac{1}{R34} \\Rz=\frac{R12*R34}{R12+R34}\\Rz=\frac{(R1+R2)(R3+R4)}{R1+R2+R3+R4}[/tex]
e)
[tex]\frac{1}{R234}=\frac{1}{R2} +\frac{1}{R3} +\frac{1}{R4} \\R234=\frac{R3*R4+R2*R4+R2*R3}{R2+R3+R4} \\Rz= R1+R234=R1+\frac{R3*R4+R2*R4+R2*R3}{R2+R3+R4}[/tex]
g)R12=R1+R2
[tex]\frac{1}{R34} =\frac{1}{R3}+\frac{1}{R4} \\R34=\frac{R3*R4}{R3+R4}=\\Rz=R12+R34=R1+R2+\frac{R3*R4}{R3+R4}\\[/tex]
i)R34=R3+R4
[tex]\frac{1}{R234} =\frac{1}{R2}+\frac{1}{R34} \\R234=\frac{R2*R34}{R2+R34}=\frac{R2*(R3+R4)}{R2+R3+R4}[/tex]
[tex]Rz=R1+R234=R1+\frac{R2*(R3+R4)}{R2+R3+R4}[/tex]
