# What is used in this derivation

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.

#### Attachments

• 22.2 KB Views: 339

Or, if you really want to go from the LHS to the RHS then use ($\frac{dA}{dt}$$)\cdot$B = $\frac{d}{dt}$(A$\cdot$B) - A$\cdot$$\frac{dB}{dt}$ which is just the product rule rearranged.