If f$1($n$)$ in $\backslash$Theta $($g$1($n$))$ and f$2($n$)$ in $\backslash$Theta $($g$2($n$)),$ then f$1($n$)+$ f$2($n$)$ in $\backslash$Theta $($g$1($n$)+$

g$2($n$)).$