$=\int _{0}^{\frac{π}{4}}\frac{\sin(x)}{\cos(x)}dx$
$=\int _{1}^{\frac{\sqrt{2}}{2}}-\frac{1}{u}du$
$=-\int _{\frac{\sqrt{2}}{2}}^{1}-\frac{1}{u}du$
$=-(-\int _{\frac{\sqrt{2}}{2}}^{1}\frac{1}{u}du)$
$=-(-[\ln\left|u\right|]_{\frac{\sqrt{2}}{2}}^{1})$
$=[\ln\left|u\right|]_{\frac{1}{\sqrt{2}}}^{1}$
$=\frac{1}{2}\ln(2)$