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I want to create a formula for summing an arithmetic sequence in which the first term is 'a1' and the nth term is 'an' through the following formula.

${{S_n}}$ = \frac{n(${{a_1}}$+${{a_n}}$)}{2}

However, the result is as follows.

enter image description here

How could I solve this problem? I am currently working on overleaf.

I'm worried that since my native language is not English and I am new to LaTeX, my question may seem a bit odd.

Mensch
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Hoon Kim
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    $S_n = \frac{n(a_1+a_n)}{2}$ is the correct input. See What are good learning resources for a LaTeX beginner? – egreg Sep 05 '22 at 22:13
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    Welcome to TeX.SX. To typeset mathematical expressions, don't enter and leave "math mode" for each symbol. $ at the beginning and again at the end. Also, you don't need so many braces: $S_n = \frac{n(a_1+a_n)}{2}$ – Sandy G Sep 05 '22 at 22:14
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    Welcome. // The problem seems to be that you switch the math mode on and off several times. In running text you type $ formulas $, i.e. just 2 $, just like opening and closing braces. Or for longer equation you start math mode by [ and end it by ] . See related links to the right for examples. – MS-SPO Sep 05 '22 at 22:16
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    A different issue: Your description of the summation sounds more to me like $S_n = \frac{n(a_1 + \ldots + a_n)}{2}$ with an ellipsis representing a₂, a₃, etc., but I might be misunderstanding. – frabjous Sep 05 '22 at 22:17
  • @frabjous $S_n = a_1+\dots+a_n = n(a_1+a_n)/2$. – Teepeemm Sep 06 '22 at 02:08
  • @Teepeemm Yeah I should have thought of that … I've even done that inductive proof. – frabjous Sep 06 '22 at 02:27

1 Answers1

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your code has a lot of unnecessary "{..}"

\documentclass{article}
\usepackage{amssymb,amsmath}

\begin{document}
[
S_{n}= \frac{n(a_1 + a_n)}{2} 
]
\end{document}

enter image description here

CrocoDuck
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