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}

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


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

  • 1
    It would be helpful if you provided the error. Also, you seem to be missing a number of \s and $s, and you've misspelled documentclass and a4paper.
    – fluffy
    Sep 9, 2013 at 22:43
  • Welcome to TeX.SX! As fluffy said, it is \documentclass, and also \lim and \frac, i.e., with backslashes.
    – mafp
    Sep 9, 2013 at 23:07

1 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}


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

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


enter image description here

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

\( \lim_{x \to 3^+} \)\( \frac{2x}{x-3} \)
  • There's also a4papter and you should have seen the relative message on the terminal. ;-)
    – egreg
    Sep 9, 2013 at 22:53

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