Answer
$$ - 5{e^{ - x}} + C$$
Work Step by Step
$$\eqalign{
& \int {5{e^{ - x}}} dx \cr
& {\text{use multiple constant rule }}\int {k \cdot f\left( x \right)} dx = k\int {f\left( x \right)} dx \cr
& = 5\int {{e^{ - x}}} dx \cr
& {\text{use the indefinite integral of an exponential function formula }}\int {{e^{kx}}} dx = \frac{{{e^{kx}}}}{k} + C \cr
& = 5\left( {\frac{{{e^{ - x}}}}{{ - 1}}} \right) + C \cr
& {\text{simplifying}} \cr
& = - 5{e^{ - x}} + C \cr} $$
