What's the difference between the first and the second?
Visually, T is located at the top right after ∑ and t = 1 is located at the bottom right after ∑ for the first one.
T is located above ∑ and t = 1 is located at the bottom of ∑ for the second one, and there is that small dot after Rit.
Is there a significant meaning to this difference or do they mean the same thing? They are from two different textbooks.