$\displaystyle \int \frac{x}{25+16x^2} dx$

$\displaystyle u=25+16x^2$

$\displaystyle du=32xdx$

$\displaystyle \frac{1}{32}du=x dx$

$\displaystyle \frac{1}{32}\int \frac{1}{u} du \rightarrow \frac{1}{32}[1] \rightarrow \frac{1}{32} + C$

Where did I go wrong or miss something?