Write a possible function rule for the following sequence.

11, 15, 19, 23, 27,

a(n)=?

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