What is this Statistical Formula Used to Calculate?

[thenokiaguru]

great forum, been looking at some past papers and saw this formula in a stats paper - don't know what it is. i want to know as it is used to calculate a question. please help...
its put up as an attachment...

or...

t = x1 - x2 / s (√ 1/n1 + 1/n2)

the x's are x bar

thanks in advance...

 

[drpizza]

Looked familiar, so I glanced around; it looks like the two-mean hypothesis test, where s_1 = s_2
(i.e. the formula I found for the two-mean hypothesis test was the same as yours, except the s was under the square root as s_1 and s_2 squared.)
Here:
http://www.duxbury.com/statistics_d/templates/student_resources/0534377556_woodbury/artfinal/Formulas/Formula%205.jpg