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I need help to understand the probability derviation of a paper. Please help me. For the following, please only treat $|h_{R,B}|^2$ and $|h_{A,R}|^2$ as random variables (other parameters can be treated as constants). Those two random varibles are i.i.d. such that they are exponential distributed with parameter $E[|h_{R,B}^2|]$ and $E[|h_{A,R}^2|]$ respectively for $|h_{R,B}|^2$ and $|h_{A,R}|^2$.

In particular, I don't understand what he did after line 74 (the yellowed part).

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