To highlight an equation, \bbox can be used. E.g,

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System of equations

• Use \begin{array}…\end{array} and \left\{…\right.. For example, you get this:

  $$
  \left\{
  \begin{array}{c}
  a_1x+b_1y+c_1z=d_1 \\
  a_2x+b_2y+c_2z=d_2 \\
  a_3x+b_3y+c_3z=d_3
  \end{array}
  \right.
  $$

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Crossing things out

Use \require{cancel} in the first formula in your post that requires cancelling; you need it only once per page. Then use:

$$\require{cancel}\begin{array}{rl}
\verb|y+\cancel{x}| & y+\cancel{x}\\
\verb|\cancel{y+x}| & \cancel{y+x}\\
\verb|y+\bcancel{x}| & y+\bcancel{x}\\
\verb|y+\xcancel{x}| & y+\xcancel{x}\\
\verb|y+\cancelto{0}{x}| & y+\cancelto{0}{x}\\
\verb+\frac{1\cancel9}{\cancel95} = \frac15+& \frac{1\cancel9}{\cancel95} = \frac15 \\
\end{array}
$$

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Fussy spacing issues

These are issues that won’t affect the correctness of formulas, but might make them look significantly better or worse. Beginners should feel free to ignore this advice; someone else will correct it for them, or more likely nobody will care.

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Arrays

It is often easier to read tables formatted in MathJax rather than plain text or a fixed width font. Arrays and tables are created with the array environment. Just after \begin{array} the format of each column should be listed, use c for a center aligned column, r for right aligned, l for left aligned and a | for a vertical line. Just as with matrices, cells are separated with & and rows are broken using \\. A horizontal line spanning the array can be placed before the current line with \hline.

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Symbols

In general, you have to search in long tables about a specific symbol you’re looking for, things like $\Psi$, $\delta$, $\zeta$, $\ge$, $\subseteq$ … And it turns out that this operation can be frustrating and time consuming, which can cause the buddy to abandon writing the complete $\LaTeX$ sentence in his answer, or in some cases, the complete answer itself.

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Aligned equations

Often people want a series of equations where the equals signs are aligned. To get this, use \begin{align}…\end{align}. Each line should end with \\, and should contain an ampersand at the point to align at, typically immediately before the equals sign.

For example,

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Matrices

1. Use $$\begin{matrix}…\end{matrix}$$ In between the \begin and \end, put the matrix elements. End each matrix row with \\, and separate matrix elements with & . For example,

   $$ \begin{matrix} 1 & x & x^2 \\ 1 & y & y^2 \\ 1 & z & z^2 \\ \end{matrix} $$

   1 2 3 4 5 6 7

   $$         \begin{matrix}         1 &  x &  x^2 \\         1 &  y &  y^2 \\         1 &  z &  z^2 \\         \end{matrix} $$

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A basic tutorial

1. To see how any formula was written in any question or answer, including this one, right-click on the expression it and choose “Show Math As > TeX Commands”. (When you do this, the ‘$’ will not display. Make sure you add these. See the next point.)

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