What is the difference between \dfrac and \frac?
Mainly it's a difference of size:
\dfrac
means that the fraction is set in displaystyle\tfrac
means that the fraction is set in textstylewith
\frac
: the actual context implies the decision above
For example, if you have a complicated mathematical expression in the middle of some array
environment (which, by default, employs text-style math), you can use \dfrac
to force the use of displaystyle math mode for the fraction
\dfrac
and \tfrac
are from the amsmath
package
Aside: TeX provides four math "styles": display style, text style, script style, and scriptscript style. scriptstyle is generally meant for level-1 subscripts and superscripts, and scriptscriptstyle is for level-2 subscripts and superscripts.
\dfrac
forces the fraction into display mode, no matter which mode it is in already. On the other hand \tfrac
forces it to be in text mode.
Usually \tfrac
is used much more than \dfrac
. Of course \frac
should be used in almost every case but \tfrac
is handy for coefficients, as shown by the code below.
\[
f(x) = \frac{1}{2} x^2 = \dfrac{1}{2} x^2 = \tfrac{1}{2} x^2
\]
$
f(x) = \frac{1}{2} x^2 = \dfrac{1}{2} x^2 = \tfrac{1}{2} x^2
$