Question

find the sum of the following series.

15 ∑ n=1 (2n+1)

a.240
b.255
c.210
d.510

Answer 1

there is some sort of formula for this, but i don't know it
on the other hand
\[\sum (2n+1)=2\sum n +\sum 1\] and \[\sum n=\frac{n(n+1)}{2}\] also
\[\sum 1=n\]

Answer 2

that gives
\[2\sum (n+1)=2\times \frac{n(n+1)}{2}+n=n(n+1)+n=n^2+2n\]

Answer 3

you're my favorite person.

Answer 4

(blush)