Question

What is the formula used to find out the first term, or thirteenth term in geometric progression?

Answer 1

do you mean this thing? \[\huge a_n = a_1 r^{n-1}\]
where
a_n = last term
a_1 = first term
r = common ratio
n = number of terms

Answer 2

or do you mean something else?

Answer 3

u can get other formulas here :
Tutorial on AP,GP,HP.
http://openstudy.com/study#/updates/503bb2a0e4b007f9003103b0

Answer 4

people still do tutorials?