typing with latex

Question

I've working on this for about two hours, but still can't find any wrong with it. This is what I type in:

\documentclas [a4papter, 12pt] {article}
\begin{document}

find \(lim_{x \to 3^+}\)\( frac{2x}{x-3}\) and \(lim_{x\to 3^-}\)\(frac{2x}{x-3}\)

\end{document}

Could anyone told me that what's the wrong with it? Thank you soooooo much.

Answer 1

You had \documentclas (a final "s" was missing) and this will cause an error. Also, you had a4papter and it should be a4paper (this will only cause a warning, but it is still an incorrection and should be taken care of).

\documentclass[a4paper, 12pt]{article}
\usepackage{amsmath}

\begin{document}

find  \(\lim_{x \to 3^+}\frac{2x}{x-3} \) and \( \lim_{x\to 3^-}\frac{2x}{x-3} \)

find  
\[
\lim_{x \to 3^+}\frac{2x}{x-3} \text{ and } \lim_{x\to 3^-}\frac{2x}{x-3}
\]

\end{document}

Notice also that you have \lim to appropriately typeset limits (correct font and spacing) and that you need \frac to typeset fractions. In my example I also show both the in-line and the displayed forms of your expression.

As long as you are in a math expression, you don't have to close math mode and reopen it, so you can simply say

\( \lim_{x \to 3^+}\frac{2x}{x-3} \)

instead of

\( \lim_{x \to 3^+} \)\( \frac{2x}{x-3} \)