Answer
$-\displaystyle \frac{1}{3}e^{-3x}+C$
Work Step by Step
Shortcut formula:
$\displaystyle \qquad \int e^{ax+b}dx=\frac{1}{a}e^{ax+b}+C$
$\displaystyle \int e^{-3x}dx=\qquad\left[\begin{array}{l}
a=-3\\
b=0
\end{array}\right]$
Apply the formula
$=\displaystyle \frac{1}{-3}e^{(-3)x+0}+C$
= $-\displaystyle \frac{1}{3}e^{-3x}+C$
