Respuesta :
If the pattern continues, so that each term is separated by a distance of 3, then the sequence is given by the recursive rule
[tex]\begin{cases}a_1=1\\a_n=a_{n-1}+3&\text{for }n>1\end{cases}[/tex]
From this definition, we can write [tex]a_n[/tex] in terms of [tex]a_1[/tex]:
[tex]a_2=a_1+3[/tex]
[tex]a_3=a_2+3=(a_1+3)+3=a_1+2\cdot3[/tex]
[tex]a_4=a_3+3=(a_1+2\cdot3)+3=a_1+3\cdot3[/tex]
[tex]a_5=a_4+3=(a_1+3\cdot3)+3=a_1+4\cdot3[/tex]
and so on, up to
[tex]a_n=a_1+(n-1)\cdot3[/tex]
(notice how the subscript on a and coefficient on 3 add up to n)
or
[tex]a_n=1+3(n-1)=3n-2[/tex]