振動回路

$\displaystyle L\frac{{di}}{{dt}}$	$\textstyle =$	$\displaystyle - \frac{q}{C}$	(31)
$\displaystyle \frac{d}{{dt}}\left( {\frac{L}{2}i^2 } \right)$	$\textstyle =$	$\displaystyle - \frac{d}{{dt}}\left( {\frac{{q^2 }}{{2C}}} \right)$	(32)
$\displaystyle \frac{d}{{dt}}\left( {\frac{L}{2}i^2 + \frac{{q^2 }}{{2C}}} \right)$	$\textstyle =$	$\displaystyle 0$	(33)