geometric and arithmetic sequences and reason

Let the sequence (`u_(n)`) defined for any natural number n by `u_(0)= -5 ` and `u_(n+1)` = `-10*u_(n)`.

1. Is (`u_(n)`) an arithmetic or a geometric sequence?
2. What is the reason of (`u_(n)`).
3. Give the expression of `u_(n)` as a function of n.