For the following exercises, suppose that $$\lim _{x \rightarrow a} f(x)=L$$ and $$\lim _{x \rightarrow a} g(x)=M$$ both exist. Use the precise definition of limits to prove the following limit laws:
$$\lim _{x \rightarrow a}[c f(x)]=c L$$ for any real constant $c$ (Hint: Consider two cases: $c=0$ and $c \neq 0 .$)