שינויים

<math>\int \frac{du}{cosu}=\int \frac{2}{1+t^{2}}\cdot \frac{1+t^{2}}{1-t^{2}}dt=\int \frac{2dt}{(1+t)(1-t)}=\int\frac{dt}{1-t}+\frac{dt}{1+t}=ln|1+t|-ln|1-t^{2}|+c=ln|1-tan^{2}\frac{u1+t}{21-t}|+c</math>