Physicists do it all the time: playing around with those symbols like [tex]\frac{dx}{dt}[/tex]. They just treat them like ordinary variables, which they certainly are not. Let me give you an example: If you want to change an integration variable from, say, x to r and you know that [tex]r^{2}=a^{2}+R^{2}-2Rx[/tex] they would simply differentiate, rearrange the stuff and write down [tex]r\cdot dr=-R\cdot dx[/tex].(adsbygoogle = window.adsbygoogle || []).push({});

Now, I don't believe this to be wrong, but I don't understand why (under what circumstances) one is allowed to operate like that. I didn't find any good answers so I thought I'd ask here.

Thanks alot in advance. Best regards

Cliowa

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# Playing around with dt, dx,

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