The first term is given when n=0
[tex]T_0=a+4(0-1)=9\Rightarrow9=a-4\Rightarrow a=13[/tex]The explicit formula is
[tex]T_n=13+4(n-1)[/tex]Note that with n=0 we obtain the first term, which is 9, and the second term is the value of Tn with n=1, which means the 9th term is given by n=8, like this
[tex]T_8=13+4(8-1)=13+4(7)=13+28=41[/tex]Therefore, the 9th term is 41.
