what is n, in the formula a(n)=a1(n-1)d
the number of terms?
but where is the "+"?
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
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
oka thhank ypu