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I'm reading a paper on foundations of QM where the expression below appeared

[itex]

\frac{1}{2}m\left(\frac{d^2 \overrightarrow{r}^2}{dt^2}\right)=m\left(\frac{d^2 \overrightarrow{r}}{dt^2}\right).\overrightarrow{r}+m\left(\frac{d \overrightarrow{r}}{dt}\right)^2

[/itex]

I cannot identify where it came from. Can you help me?

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# Unknown expression

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