An arithmetic sequence (a_n) is as follows:
[tex]a_1\\a_2=a_1+d\\a_3= a_1+2d\\a_4=a_1+3d,...[/tex] where [tex]a_1[/tex] is the first term and d is the constant difference,
thus, we see that the n'th term of an arithmetic sequence is [tex]a_n=a_1+(n-1)d[/tex]
in our particular case d=5, the third term is 8, so we have:
[tex]a_3=8=a_1+2\cdot5\\\\8=a_1+10\\\\a_1=-2[/tex]
and the general term is [tex]a_n=-2+5(n-1)[/tex],
Answer: first term is -2, n'th term is -2+5(n-1)
