#R_1" and "R_2" are connected as serial"#
#R_6=R_1+R_2" ; "R_6=1+4=5" "Omega#
#R_4" and "R_5" are connected serial"#
#R_7=R_4+R_5" ; "R_7=2+3=5 " "Omega#
#R_6" , "R_3" , "R_7" are connected as parallel"#
#1/R_"AB"=1/R_6+1/R_3+1/R_7#
#1/R_"AB"=1/5+1/1+1/5#
#1/R_"AB"=(1+5+1)/5#
#1/R_"AB"=7/5#
#R_"AB"*7=5#
#R_"AB"=5/7" "Omega#