Answer:
Step-by-step explanation:
The explicit formula for an arithmetic sequence is
[tex]a_n=a_1+d(n-1)[/tex]
where n is the position of the number in the sequence, a1 is the first number in the sequence, and d is the common difference between the numbers.
If we are looking for the 91st term, our n = 91;
our a1 is 28, and
the common difference is -20. Putting all that together gives us the explicit formula for this sequence:
[tex]a_{91}=28-20(91-1)[/tex] and
[tex]a_{91}=28-20(90)[/tex] and
[tex]a_{91}=28-1800[/tex] so
[tex]a_{91}=-1772[/tex]
