Im trying to follow another example in this book, and im not sure how the following is done

$\displaystyle \frac{d^2x}{dr^2} + \frac{1}{r} * \frac{dx}{dr}- \frac{x}{r^2} = \frac{Q}{D} $

apprantley can be rearanged as follows:

$\displaystyle \frac{d}{dr} [ \frac{1}{r} * \frac{d}{dr} (xr) ] = \frac{Q}{D} $

Thanks in advance

Calypso