Question

what is n, in the formula a(n)=a1(n-1)d

Answer 1

the number of terms?

Answer 2

but where is the "+"?

Answer 3

idk

Answer 4

this looks like the formula for getting the n'th term of an arithmetic sequence (or progression). this site might help you understand this better: http://en.wikipedia.org/wiki/Arithmetic_progression

Answer 5

n is any term numbers that you plug in. Take a look at this and let me know.
http://www.mathwords.com/a/arithmetic_sequence.htm

Answer 6

oka thhank ypu