Math CentralQuandaries & Queries


Question from Juan, a student:

In an arithmetic sequence, the first term is -2, the fourth term is 16 and the nth
term is 11,998
A. What is the common difference?

B. What is the value of n.

Hi Juan,

The formula for arithmetic sequence is an=a1+(n-1)d where a1 is the first term, an is the nth term in the sequence and d is the common difference.

So for the fourth term we can write it as


What is the value of d? Once d is found, you can use the same formula for the nth term 11998 to find how many terms are in the sequence.

Hope this helps,


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