Geometry LaTeX Tips

When in doubt, it's better to use more words and less notation. But the examples below might be helpful if you want to use notation. I've written out a lot of the LaTeX code in plain text, but you can click on "Edit" explanation (and click on different paragraphs) to directly see or copy the LaTeX code.

Lines

• Some common line names are $l,m,n$ (sometimes with subscripts, like $l_1$ or $l_2$, if you have lots of lines).
• When you have two or more points on the lines, say $A$ and $B$, you can also describe the line using those points: "line/segment/ray $AB$" is simplest.

Angles, Parallel, Perpendicular, Congruent/Similar

• Degrees: $90^\circ$ is "90^\circ", same for any other angle
• Angle $\angle$ is "\angle " (with a space to be safe), like $\angle ABC$ or $\angle 1$
• Some people emphasize angle measures (as opposed to angle names) by writing $m\angle$, which is "m\angle " (again with a space)
• Parallel lines: $l\parallel m$ is "l \parallel m" (with a space to be safe)
• Perpendicular lines: $l\perp m$ is "l \perp m" (with a space to be safe)
• Congruence: $\cong$ is "\cong " (with a space to be safe)
• Similarity: $\sim$ is "\sim " (with a space to be safe). I don't remember if anyone actually uses this notation though.

Templates you can copy (click Edit explanation and then click on this paragraph to see the code)

The following are true:

• If $\ell\parallel m$ and $m\parallel n$, then $\ell\parallel n$.
• If $\ell\perp m$ and $m\perp n$, then $\ell\parallel n$.
• If $\ell\perp m$ and $m\parallel n$, then $\ell\perp n$.
• Suppose $AB\perp BC$ and segment $AD$ is perpendicular to segment $CD$ (given). Then $m\angle{ABC} = m\angle{B} = \frac{\pi}{2} = 90^\circ$. This means $\angle{ABC}$ is right and $\triangle{ABC}$ is a right triangle. Similarly, angle $ADC$ is right and triangle $ADC$ is a right triangle. Also, since $m\angle{ABC} = m\angle{ADC}$, angles $ABC$ and $ADC$ are congurent: in notation, $\angle{ABC} \cong \angle{ADC}$.

Fancier things, don't worry about this unless you really want to

• $\triangle{ABC}$ is "\triangle ABC" or "\triangle{ABC}" (you just need a space or brackets so that the end of \triangle doesn't get confused with the beginning of ABC). This is different than "\Delta{y}/\Delta{x}" in slopes: $m = \Delta{y}/\Delta{x}$.
• Pretty $\ell$ is "\ell"
• Some people use "\overline{AB}" for lines, like $\overline{AB}$, or "\overrightarrow{AB}" $\overrightarrow{AB}$ for rays.