In the circuit shown in the figure `R_(X)` is a variable resistance. find the equivalent resistance `(R_(AB))` between A and B in terms of `R and R_(X)`. What are the possible range of values of `R_(AB)` ?

Answer

(a) `R_(AB)=((4R+3R_(x))/(3R+2R_(x)))R`
`(4)/(3) R lt R_(AB) lt (3)/(2)R`