\( \int \cos (x) \cdot e^{\sin (x)} d x \)
mit u=sin(x) hast du  \(  \frac{du}{dx} = u' = cos(x)   \) und
damit   \(  dx = \frac{du}{cos(x)}  \). Also
\( \int \cos (x) \cdot e^{\sin (x)} d x = \int \cos (x) \cdot e^{u} \frac{du}{cos(x)} = \int  e^{u} du \) 
\( =  e^{u}+C = e^{sin(x)} + C\)