array1: sample from the first population
array2: sample from the second population
tails: number of tails to consider
type: Type of test to perform. 1 indicates a test for paired variables, 2 a test of unpaired variables with equal variances, and 3 a test of unpaired variables with unequal variances
If the data sets contain a different number of data points and the test is paired (type one), TTEST returns the #N/A error. tails and type are truncated to integers. If tails is not one or two, this function returns a #NUM! error. If type is any other than one, two, or three, this function returns a #NUM! error.
This function is Excel compatible.