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What is used in this derivation

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  • #1
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Consider the equation on the attached picture. What mathematical identity for differential calculus (which I assume is used) is used to go from the LHS to the RHS? I tried invoking the product rule but couldn't get anywhere.
 

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  • #2
TSny
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You're on the right track. Apply the product rule to the first term on the RHS and show that the entire RHS reduces to the LHS.
 
  • #3
TSny
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Or, if you really want to go from the LHS to the RHS then use ([itex]\frac{dA}{dt}[/itex][itex])\cdot[/itex]B = [itex]\frac{d}{dt}[/itex](A[itex]\cdot[/itex]B) - A[itex]\cdot[/itex][itex]\frac{dB}{dt}[/itex] which is just the product rule rearranged.
 
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