Write down the partition function for a single segment ZN=1 of a FreelyJointed-Chain in one dimension subjected to force.

Hello, please How to solve this one!!! Write down the partition function for a single segment ZN=1 of a FreelyJointed-Chain in one dimension subjected to force. For N such segments the partitionfunction scales as: Z_N = (Z_N=1)^N . Using the differentiation trick: <L> =1/β)∂ ln(Z)/∂f reproduce the expression for the force extension behavior derived in the lecture.