Zeroth law of thermodynamic and definition of temperature

[Binvestigator]

Hello everybody, I am a new member and do not know what is the best way to asking question.
in "statistical physics of particle , m.kardar" .
how he derived eq1.6 ?
he said that we can eliminate "C" from eq1.4, but how?
http://libgen.org/book/index.php?md5=BC07A3BDB70689E0E612DED12C96CC78
the book can be downloaded from above address.

 

[cwasdqwe]

Can you please add a screenshot or similar? Thanks