Texas Instruments TI-NSPIRE Software Manual page 240

geometcdf (geomCdf())
x
computes a cumulative probability at , the number of the
geometcdf (
trial on which the first success occurs, for the discrete geometric
p p
1 must be
distribution with the specified probability of success . 0
x
true. can be a real number or a list of real numbers.
This distribution is useful in determining the probability associated with
the first success occurring during trials 1 through n. For example, you
could use this calculation to determine the probability that heads display
on toss #1, #2, #3, ..., #n.
228 Using Lists & Spreadsheet