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I have this thermodynamical expression:

[itex]dS=\sigma T^3 dV+4V\sigma T^2 dT+\frac{1}{3}\sigma T^3 dV=d(\frac{4}{3}\sigma T^3 V)[/itex]

Basically saying:

[itex]\frac{4}{3}\sigma T^3 V=S[/itex]

Now, I do not get this.. d(expr) part, why are there three members to d(expr), with 2x dV and 1x dT.. nope..

I might add that [itex]\sigma[/itex] is a constant.

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# Differential, why three members

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