Interpreting these given formulas...

Question

I am writing a program for an assignment in which I need to incorporate these two formulas; but, the problem is, I have no understanding of the formatting of these formulas and I am just at a loss with what I could find online.

Maybe the question I should be asking is, "What kind of formatting is being used for those formulas and what does each part mean?"

I apologize for lack of clarity and for my confusion -- I've been dealing with trying to figure this out for weeks, on and off, and use Stack Exchange as a last resort.

Below is a screenshot attachment.

Edit: And I did see this other post, but it confuses me. I haven't made it that far in math.

Answer 1

In mathematics, $\sum$ often means "sum", and the term

$$\sum_{i=1}^n a_i$$

is read as "the sum of all $a_i$ where $i$ goes from $1$ to $n$, in other words

$$\sum_{i=1}^n a_i = a_1 + a_2 + \cdots + a_n$$

Answer 2

The formula for the mean means that you need to take the sum of all values and divide by the number of values.

The second says that you take the sum of the squares of the values, divide by the number of values and subtract the square of the above mean.