quotient rule

$\frac{d}{dx}\frac{f(x)}{g(x)}=\frac{f^{\prime }\cdot g(x)-f(x)\cdot g^{\prime }(x)}{g(x{)}^2}$

$\frac{d}{dx}\frac{\mathrm{high}}{\mathrm{low}}=\frac{\mathrm{low}(\mathrm{d}\cdot \mathrm{high})-\mathrm{high}(\mathrm{d}\cdot \mathrm{low})}{\mathrm{low}\cdot \mathrm{low}}$