Hi Chris,
you can either use delimiters for displaystyle (propabably \[...\]) or you put \displaystyle at the beginning of your expression. This will give \[\lim_{x \to a}[k\cdot f(x)] = k\lim_{x\to a}f(x)=kA\] respectively \(\displaystyle \lim_{x \to a}[k\cdot f(x)] = k\lim_{x\to a}f(x)=kA\).
Stephan