The first thing we are going to to is checking if the sequence is arithmetic of geometric. A sequence is arithmetic if it has a common difference, 
. A sequence is geometric if it has a common ratio, 
.
Lets test for a common difference first. To do that we are going to subtract the current term from the previous term:
Since we have a common difference,
, or sequence is arithmetic.
Now, to find its 105 term, we are going to find its explicit formula using the general form of an arithmetic sequence:
where
is the nth term
is the first term
is the position of the term in the sequence
is the common diference
We can infer for our sequence that
, and for previews calculations we know that . So lets replace those values:
Finally, to find the 105th term of the sequence, we just need to replace with 105 in our explicit formula:
We can conclude that the 105th term of the sequence is -395.
Lets test for a common difference first. To do that we are going to subtract the current term from the previous term:
Since we have a common difference,
Now, to find its 105 term, we are going to find its explicit formula using the general form of an arithmetic sequence:
where
We can infer for our sequence that
Finally, to find the 105th term of the sequence, we just need to replace
We can conclude that the 105th term of the sequence is -395.