\[\begin{array}{l}
 T1. \to \int {} dx = x + C\,\,\,\, \\ 
 {\rm{Dokaz}}\,{\rm{(Proof):}} \\ 
 \int {dx}  = \int {\frac{{{x^n}}}{{{x^n}}}} dx = \int {{x^n}{x^{ - n}}} dx = \left| {\begin{array}{*{20}{c}}
   {dv = {x^n}dx} & {u = {x^{ - n}}}  \\
   {v = \frac{{{x^{n + 1}}}}{{n + 1}}} & {du =  - n{x^{ - n - 1}}dx}  \\
\end{array}} \right| = {x^{ - n}}\frac{{{x^{n + 1}}}}{{n + 1}} + \frac{n}{{n + 1}}\int {{x^{n + 1}}{x^{ - n - 1}}dx}  = \frac{{{x^n}x}}{{{x^n}(n + 1)}} + \frac{n}{{n + 1}}\int {dx}  \\ 
 \int {dx}  - \frac{n}{{n + 1}}\int {dx}  = \frac{x}{{n + 1}} \\ 
 \left( {1 - \frac{n}{{n + 1}}} \right)\int {dx}  = \frac{x}{{n + 1}} \\ 
 \left( {\frac{1}{{n + 1}}} \right)\int {dx}  = \frac{x}{{n + 1}} \\ 
 \int {dx}  = x + C \\ 
 \end{array}\]