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How do I use TeX?

For inline formulas place your TeX between single dollar signs and for block level formatting place the TeX between double dollar signs.

For example, \$x = \dfrac{-b \pm \sqrt{b^2-4ac}}{2a}\$ produces $x = \dfrac{-b \pm \sqrt{b^2-4ac}}{2a}$.

For a useful guide on formatting using TeX visit: http://en.wikipedia.org/wiki/Help:Displaying_a_formula#Formatting_using_TeX

Handy Tip: If you are wondering how someone produced a nice effect in his/her post then click Quote and you will be able to see how it is done. (c;

How do I get the [code] tag to display my language?

If no language is specified then the script will use the "preferred language" in your profile automatically. However, if your language is not currently supported then the script will auto-detect. You can override the selected language by using [code=_language_], but in the same way if it is not a currently supported language then the script will auto-detect. You can force auto-detect by using [code=?] or you can disable highlighting completely by using [code=*]. Both of these can be used in conjunction with specifying a language. For example, if your preferred language was PHP you could use [code=basic*] and it would display the language name BASIC at the top of the code block, but highlighting would be disabled; similarly with using ? for auto-detect.

Can I use HTML in my posts?

Unfortunately not. However, many of the features you would like to use, such as links, images, emboldened text, colours, and so on, can be achieved using custom tags. A list of the effects and the required custom tags are given in the table below. Please note that all custom tags must be in lowercase.

Effect
Code
PHP
Show Code
$s = array("Cool", "Awesome", "Fantastic");
$r = array_rand($s);
print "Project Euler is " . $s[$r];
[code]
\$s = array("Cool", "Awesome", "Fantastic");
\$r = array_rand(\$s);
print "Project Euler is " . \$s[\$r];
[/code]
Obvious is the most dangerous word in mathematics.
[quote]Obvious is the most dangerous word in mathematics.[/quote]
Expand
This tag is ideal for spoilers or lengthy blocks of text (for example, proofs or program output) that might detract from your otherwise punchy, perfect post. (c;
[collapse]
This tag is ideal for spoilers or lengthy blocks of text (for example, proofs or program output) that might detract from your otherwise punchy, perfect post. (c;
[/collapse]
How Not To Solve Quadratics
Expand
If $ax^2 + bx + c = 0$, then $$x \ne \dfrac{b \pm \sqrt{b^2 - 4ac}}{2a}$$
[collapse=How Not To Solve Quadratics]
If \$ax^2 + bx + c = 0\$, then
\$\$x \ne \dfrac{b \pm \sqrt{b^2 - 4ac}}{2a}\$\$
[/collapse]
Peekaboo! [hide]Peekaboo![/hide]

Hover mouse over hidden text to reveal

Italic [i]Italic[/i]
Bold [b]Bold[/b]
Strike-through [s]Strike-through[/s]
Red and Green [r]Red[/r] and [g]Green[/g]
   Tab 1
      Tab 2
         Tab 3
[t1]Tab 1 (each tab inserts three spaces)
[t2]Tab 2
[t3]Tab 3
Project Euler [url=https://projecteuler.net]Project Euler[/url]
https://projecteuler.net [url]https://projecteuler.net[/url]
[img]https://projecteuler.net/images/print_page_logo.png[/img]
In the middle of things
[center]In the middle of things[/center]
Superscript [sup]Super[/sup]script
Subscript [sub]Sub[/sub]script
√ (root) [radic]
∑ (sum) [sum]
≡ (equivalent) [equiv]
≈ (approx) [asymp]
∴ (therefore) [there4]
± (plus/minus) [plusmn]