An arithmetic sequence has the form as
[tex]a_n=a_1+(n-1)d[/tex]
where [tex]a_n[/tex] = n-th term,
[tex]a_1[/tex] = first term,
d = common difference
We can see that 11 – 9 = 13 – 11 = 15 – 13 = 2. So the common difference is d = 2.
The first term is [tex]a_1=9[/tex]. So the n-th term of the sequence is
[tex]a_n=9+(n-1)(2)=9+2n-2=7+2n[/tex]
So the answer is [tex]a_n=7+2n[/tex]
