Question

What is the 5th partial sum of Infinity sigma n=1
-2+5n

Answer 1

\[\sum_{n=1}^{m}(5n-2)=\frac12(5m^2+m)\]
\[\therefore \frac12(5(5^2)+5)=65\]
Alternatively... you can do it the long way:
\[(5(1)-2)+(5(2)-2)+(5(3)-2)+(5(4)-2)+(5(5)-2)=65\]