Editing Chi-squared distribution (section)

=== Probability density function ===
The [[probability density function]] (pdf) of the chi-squared distribution is
:<math>
f(x;\,k) =
\begin{cases}
  \dfrac{x^{k/2 -1} e^{-x/2}}{2^{k/2} \Gamma\left(\frac k 2 \right)}, & x > 0; \\ 0, & \text{otherwise}.
\end{cases}
</math>
where <math display="inline">\Gamma(k/2)</math> denotes the [[gamma function]], which has [[particular values of the gamma function|closed-form values for integer <math>k</math>]].

For derivations of the pdf in the cases of one, two and <math>k</math> degrees of freedom, see [[Proofs related to chi-squared distribution]].