Rewrite ... logF=logG+logH−log(1/M)−2*logR ... in the form F=... using laws of logarithms

logF=logG+logH−log(1/M)−2*logR Simplify RHS using law of logarithms, 

logF=log(GH)−log(1/M)−2logR             using law of addition
logF=log(GHM)−2logR                      using law of subtraction
logF=log((GHM)/R^2))                        using law of powers and subtraction so by taking logs of both sides we have:

F = (GHM) / R^2