# TI-BASIC:Invt

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**Command Summary**

Calculates the inverse of the cumulative [*https://en.wikipedia.org/wiki/Student%27s_t-distribution Student's t-distribution] function with degrees of freedom ν.

**Command Syntax**

invT(*probability*, *ν*)

**Menu Location**

Press:

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

TI-84+/SE (OS 2.30 or greater)

2 bytes

invT( is the inverse of the cumulative Student t distribution function: given a probability *p* and a specified degrees of freedom *ν*, it will return the number *x* such that tcdf(-E99,*x*,*ν*) is equal to *p*

:invT(.95,24 1.710882023

# Advanced

invT( is meant for use with so-called "one-tailed' tests; for two-tailed tests, the proper expression to use (corresponding to the inverse of tcdf(-*x*,*x*,*ν*)) is invT(.5(1+*p*),*ν*)

# Formulas

Unlike the Tpdf( and Tcdf( commands, the invT( command does not have a closed-form formula. However, it can be expressed in terms of the inverse incomplete beta function.

For one degree of freedom, invT( is expressible in terms of simpler functions:

<math> \definecolor{darkgreen}{rgb}{0.90,0.91,0.859}\pagecolor{darkgreen} \operatorname{invT}(p,1)=\tan\left(\pi\left(p-\frac1{2}\right)\right) </math>