# TI-BASIC:Chisquarepdf

**Command Summary**

Evaluates the χ² probability density function at a point.

**Command Syntax**

χ²pdf(*x*, *df*

**Menu Location**

Press:

- 2ND DISTR to access the distribution menu
- 6 to select χ²pdf(, or use arrows.

Press 7 instead of 6 on a TI-84+/SE with OS 2.30 or higher.

TI-83/84/+/SE

2 bytes

χ²pdf( is the χ² probability density function.

Since the χ² distribution is continuous, the value of χ²pdf( doesn't represent an actual probability -- in fact, one of the only uses for this command is to draw a graph of the χ² curve. You could also use it for various calculus purposes, such as finding inflection points.

The command takes two arguments: the value at which to evaluate the p.d.f., and *df*, the number of 'degrees of freedom'.

# Formulas

The value of χ²pdf( is given by

<math> \definecolor{darkgreen}{rgb}{0.90,0.91,0.859}\pagecolor{darkgreen} \operatorname{\chi^2pdf}(x,k)=\frac{(1/2)^{k/2}}{(k/2-1)!}\,x^{k/2-1}e^{-x/2} </math>