ah, so an aritmetic sequence can be written in form
[tex]a_n=a_1+d(n-1)[/tex]
where [tex]a_n[/tex] is the nth term
[tex]a_1[/tex] is the first term
d is the common difference or how many times it increase or decreases each day
so an example:
Bob swims 2 miles on one day. Every day, he increases his distance by 0.2 miles. If he continues this pattern, how many miles will he swim on the 7th day?
[tex]a_n=a_1+d(n-1)[/tex]
[tex]a_7=2+0.2(7-1)[/tex]
[tex]a_7=2+0.2(6)[/tex]
[tex]a_7=2+1.2[/tex]
[tex]a_7=3.2[/tex]
bob swims 3.2 miles on the 7th term
also, you can use f(n) instead of [tex]a_n[/tex]