5.1 Writing formulas in TeX

From Förberedande kurs i matematik 1

Revision as of 12:28, 27 January 2009

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
Don't write	sin x	sinx
Don't write	\sinx	Error
Do write	\sin x	sinx
Don't write	4*3	43
Do write	4\times 3	43
Don't write	a\times b	ab
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
Don't write	a2	a2
Do write	a^2	a2
Don't write	x1	x1
Do write	x_1	x1
Don't write	a^22	a22
Do write	a^{22}	a22
Don't write	30^{o}	30o
Don't write	30^{0}	300
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
Don't write	(1-(1-x)	(1−(1−x)
Do write	(1-(1-x))	(1−(1−x))
Don't write	(\dfrac{a}{b}+c)	(ba+c)
Do write	\left(\dfrac{a}{b}+c\right)	ba+c
Don't write	\frac(1)(2)	(1)(2)
Do write	\frac{1}{2}	21
Don't write	\sqrt(a+b)	(a+b)
Don't write	\sqrt{(a+b)}	(a+b)
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
Don't write	\dfrac{1}{2}	21
Do write	\frac{1}{2}	21
(Exception: If the fraction is next to a large expression you should, however, write the fraction as a large fraction.)
Don't write	\frac{a}{b}	ba
Do write	\dfrac{a}{b}	ba
Don't write	\frac{\sqrt{3}}{2}	23
Do write	\dfrac{\sqrt{3}}{2}	\displaystyle \dfrac{\sqrt{3}}{2}
Don't write	a^{\frac{1}{2}}	\displaystyle a^{\frac{1}{2}}
Do write	a^{1/2}	\displaystyle a^{1/2}