Given:
The geometric sequence is:
1 -4
2 20
3 -100
To find:
The explicit formula and list any restrictions to the domain.
Solution:
The explicit formula of a geometric sequence is:
...(i)
Where, a is the first term, r is the common ratio and .
In the given sequence the first term is -4 and the second term is 20, so the common ratio is:
Putting in (i), we get
where
Therefore, the correct option is B.