Verified answer

[tex]1)\\R_2+R_5=2+2=4Om\\R_8+R_{11}=2+2=4Om\\\\2)\\R_{2,4,5}=\frac{R_4*R_{2,5}}{R_4+R_{2,5}+R_7} =\frac{2*4}{2+4+2} =1Om\\R_{2,5,7}=\frac{R_7*R_{2,5}}{R_4+R_{2,5}+R_7} =\frac{2*4}{2+4+2} =1Om\\R_{4,7}=\frac{R_7*R_{4}}{R_4+R_{2,5}+R_7} =\frac{2*2}{2+4+2} =0.5Om\\\\R_{6,8,11}=\frac{R_6*R_{8,11}}{R_6+R_{8,11}+R_9} =\frac{2*4}{2+4+2} =1Om\\R_{8,9,11}=\frac{R_9*R_{8,11}}{R_6+R_{8,11}+R_9} =\frac{2*4}{2+4+2} =1Om\\R_{6,9}=\frac{R_6*R_{9}}{R_6+R_{8,11}+R_9} =\frac{2*2}{2+4+2} =0.5Om\\\\[/tex]

[tex]3)\\R_{4,6,7,9}=R_{6,9}+R_{4,7}=0.5+0.5=1Om\\\\R_{1,2,4,5}=R_1+R_{2,4,5}=2+1=3Om\\R_{10,2,5,7}=R_{10}+R_{2,5,7}=2+1=3Om\\R_{3,6,8,11}=R_3+R_{6,8,11}=2+1=3Om\\R_{8,9,11,12}=R_{12}+R_{8,9,11}=2+1=3Om\\\\4)\\R_{3,6,8,9,11,12}=R_{3,6,8,11}+R_{8,9,11,12}+\frac{R_{3,6,8,11}*R_{8,9,11,12}}{R_{4,6,7,9}} =3+3+\frac{3*3}{1}=15Om \\R_{3,4,6,7,8,9,11}=R_{3,6,8,11}+R_{4,6,7,9}+\frac{R_{3,6,8,11}*R_{4,6,7,9}}{R_{8,9,11,12}} =3+1+\frac{3*1}{3}=5Om \\[/tex]

[tex]R_{4,6,7,8,9,11,12}=R_{8,9,11,12}+R_{4,6,7,9}+\frac{R_{8,9,11,12}*R_{4,6,7,9}}{R_{3,6,8,11}} =3+1+\frac{3*1}{3}=5Om\\\\5)\\R_{3,4,6,7,8,9,11,12}=5+5=10Om\\R_{1,2,4,5,7,10}=3+3=6Om\\\\6)\\R_{3,4,6,7,8,9,11,12}=\frac{15*10}{15+10}= 6Om[/tex]

Rзаг =  [tex]\frac{6*6}{6+6}=3 Om[/tex]