I have a more general question to ask:
about using the $\cdots$ symbol.
As far as I have heard three dots will represent that it continues up to infinity.
And I have found (mostly in computer programming) that two dots will be used in a case to indicate the terms between two specific points.
So my question is what is suitable to write in a case where finite number of terms are used.
For example Consider the set with $n$ number of elements. Let them be
$$x_1,x_2, \cdot \cdot x_n \;\text{ two dots. }$$ Or is it $$x_1,x_2, \cdots x_n\;\;?$$
You'll need to use three dots:
$\{1, 2, 3, \ldots \}$
$\{1, 2, \ldots, 10\}$
You can also use three dots to indicate an infinite sum, or to abbreviate the sum of many numbers, provided you've made the pattern clear.
$\sum_{k = 1}^{k=119} k = 1 + 2+ 3+ \cdots + 119\\$
$\sum_{k=1}^\infty k =1 + 2 + 3 + \cdots$