\[\begin{array}{l}
 T7. \to \int {\cos xdx}  = \sin x + C \\ 
 {\rm{Dokaz}}\,{\rm{(Proof):}} \\ 
 \int {\cos xdx}  = \left| \begin{array}{l}
 \sin x = t \\ 
 \cos xdx = dt \\ 
 \end{array} \right| = \int {dt}  = t = \sin x \\ 
 \end{array}\]