What's the n-th term of a geometric sequence given by?
well if it is a geometric series with common ratio 1/3 then to obtain the next term from the one you have you multiply by 1/3 so if your first term is -2 you multiply this by 1/3 to get the next term and so on so the n-th term is equal to the first term ( -2) multiplied by 1/3 n times which equal (1/3)^n