Calculus with Applications (10th Edition)

see: Rules for Limits Let $a, A$, and $B$ be real numbers, and let $f$ and $g$ be functions such that $\displaystyle \lim_{x\rightarrow a}f(x)=A$ and $\displaystyle \lim_{x\rightarrow a}g(x)=B$. 2. $\displaystyle \lim_{x\rightarrow a}[f(x)\pm g(x)]=\lim_{x\rightarrow a}f(x)\pm\lim_{x\rightarrow a}g(x)=A\pm B$ (The limit of a sum or difference is the sum or difference of the limits.) --------------- $\displaystyle \lim_{x\rightarrow 4}[f(x)-g(x)]=\lim_{x\rightarrow 4}f(x)-\lim_{x\rightarrow 4}g(x)$ $=9-27=-18$