The equation says: d(lnW)=Ʃ[itex]_{i}[/itex](dlnW[itex]_{i}[/itex]/dN[itex]_{i}[/itex])*dN[itex]_{i}[/itex](adsbygoogle = window.adsbygoogle || []).push({});

I chose the constants as so since I ran across this in a Physical problem, but it doesn't matter. It is the maths that I don't understand.

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# I don't get this expansion

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