Verify the identity using differentiation.

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{x}{(4x^2+5{)}^2}dx=-\frac{1}{8(4x^2+5)}$

$\frac{d}{dx}(-\frac{1}{8(4x^2+5)})=$

Using the indicated $u-$substitution, identify $f$ such that the integral takes the form ${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}f(u)du.$

$f(u)=$