Question

Write a possible function rule for the following sequence.

11, 15, 19, 23, 27, ...

a(n)=?

Answer 1

This is an arithmetic sequence because a common difference exists. The common difference is a constant found when taking any term and subtracting the previous term from it. In this case the common difference is 4, meaning that each term is 4 units greater than the previous term. Any arithmetic sequence can be expressed as:

a(n)=a+d(n-1), a=initial term, d=common difference, n=term number

In this case we know a=11 and d=4 so

a(n)=11+4(n-1) which can be simplified...

a(n)=11+4n-4

a(n)=4n+7

Answer 2

a(n) = 4(n - 1) + 11 is the equation because a(1) = 11 and the common difference (d) = 4. Then you just plug it into the arithmetic sequence formula which is a(n) = d(n - 1) + a(1). I hope this was helpful.