It's a arithmetic sequence
- First term=a=3
- common difference=d=-1-3=-4
Nth term rule:-
[tex]\\ \rm\Rrightarrow a_n=a+(n-1)d[/tex]
[tex]\\ \rm\Rrightarrow a_n=3+(n-1)-4[/tex]
[tex]\\ \rm\Rrightarrow a_n=3-4n+4[/tex]
[tex]\\ \rm\Rrightarrow a_n=7-4n[/tex]
20th term
[tex]\\ \rm\Rrightarrow a_{20}=7-80=-73[/tex]
