If I evaluate an integral
$\displaystyle \int {1 \over 3x}dx = \ln {3x} + \ln c $
or the constant can be brought outside: $\displaystyle \int {1 \over 3x}dx = {1 \over 3}\int {1 \over x} dx = {1 \over 3} \ln x + \ln c$
which are different answers, how is this?