posted by Kevin .
To find the nth term of an arithmetic sequence the formula given is a(sub n) = a (sub 1) + (n-1)d. Why is (n-1) a part of the formula? Why isn't just n?
Remember d is your pattern, or what you are adding, to get each term. You are starting with the first term, so when you add 1 time, you reach the 2nd term. THen when you add again (2 times) you are up to the 3rd term. When you add again (3 times) you move to the 4th term. Do you see the pattern of how you add one less time then the term you end up finding? That is the (n-1)