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5.1 Writing formulas in TeX

From Förberedande kurs i matematik 1

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Contents:

  • What is TeX/LaTeX?
  • Common expressions
  • Common mistakes

Learning outcomes:

After this section you will have learned how to:

  • Write formulas in TeX

What is TeX/LaTeX?

Common expressions

Common mistakes

One of the most common mistakes when editing math in the wiki is to forget the start <math> tag and the end </math> tag.

Remember also to start commands with a backslash (\) and to add a space after the commands (unless they are followed immediately by a new command).

Another frequent mistake is to use an asterisk (*) instead of a proper multiplication sign (\times in TeX).

Example

TeX Result
  1. Don't write
sin x sinx
  1. Don't write
\sinx Error
  1. Do write
\sin x sinx
  1. Don't write
4*3 43
  1. Do write
4\times 3 43
  1. Don't write
a\times b ab
  1. Do write
ab ab

Exponents and indices

When writing exponents you use ^ followed by the exponent and to write indices you use _ followed by the index. If the exponent or index consists of more than one symbol it must be enclosed with braces {}.

A special kind of exponent is the degree sign (°) which is written as ^{\circ}.

Example

TeX Result
  1. Don't write
a2 a2
  1. Do write
a^2 a2
  1. Don't write
x1 x1
  1. Do write
x_1 x1
  1. Don't write
a^22 a22
  1. Do write
a^{22} a22
  1. Don't write
30^{o} 30o
  1. Don't write
30^{0} 300
  1. Do write
30^{\circ} 30

Delimiters

In more complex expressions you need to make sure to balance each opening parenthesis ( with a closing parenthesis ).

A pair of parenthesis that delimits a tall expression should be as large as the expression. You should therefore prefix the opening parenthesis with \left and the closing parenthesis with \right to get a pair of extensible parentheses that adjust its height to the expression.

Note also that braces {} and not parentheses () are used in commands to delimits arguments.

Example

TeX Result
  1. Don't write
(1-(1-x) (1−(1−x)
  1. Do write
(1-(1-x)) (1−(1−x))
  1. Don't write
(\dfrac{a}{b}+c) (ba+c)
  1. Do write
\left(\dfrac{a}{b}+c\right) ba+c 
  1. Don't write
\frac(1)(2) (1)(2)
  1. Do write
\frac{1}{2} 21
  1. Don't write
\sqrt(a+b) (a+b) 
  1. Don't write
\sqrt{(a+b)} (a+b) 
  1. Do write
\sqrt{a+b} a+b 

Fractions

As a rule of thumb you should write fractions where the numerator and denominator consist only of a few digits as a small fraction (i.e. with \tfrac), while other fractions should be large (i.e. with \frac).

If an exponent or index contains a fraction then that fraction should be written in a slashed form (e.g. 52 instead of 25) to enhance the legibility.

Example

TeX Result
  1. Don't write
\dfrac{1}{2} 21
  1. Do write
\frac{1}{2} 21
  1. (Exception: If the fraction is next to a large expression you should, however, write the fraction as a large fraction.)
  1. Don't write
\frac{a}{b} ba
  1. Do write
\dfrac{a}{b} ba
  1. Don't write
\frac{\sqrt{3}}{2} 23 
  1. Do write
\dfrac{\sqrt{3}}{2} \displaystyle \dfrac{\sqrt{3}}{2}
  1. Don't write
a^{\frac{1}{2}} \displaystyle a^{\frac{1}{2}}
  1. Do write
a^{1/2} \displaystyle a^{1/2}


Study advice

Useful web sites

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