Solving a pseudo-steady state mixed mode

Solving a pseudo-steady state mixed mode 

Taking again our mechanism made up of the steps from [7.Et.bl] to [7.Et.bn+l] and assuming that steps i and j are the rate-determining steps (their rate constants are the only ones with finite values). Considering the two steps, one that follows the first rate-determining step (step [7.Et.bi+l]) and second that precedes the second ratedetermining step (step [7.Et.bj-l]). 

According to the properly of a pseudo-steady state mode, we can write the rate in the two forms  

Concentration [X, J is calculated by considering that all the preceding steps are at equilibrium, thus, according to equation [7.39]  

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