13-6

13-6 is all about sigmas. A sigma is simply a series written in condensed form. Since I'm not fancy with my computer I'm going to use an E to represent a sigma and I will try to express the rest as best as I can.

On the top of the sigma is the limit of summation (#). Underneath the sigma is where the index is placed (n). And to the right is the summand (f(x)).
Example
7
E 2k
k=1

Here the limits are 7 and 1
The summand is 2k
The index is k

In order to evaluate the sigma replace k with the numbers 1-7 like so
2*1+2*2+2*3+2*4+2*5+2*6+2*7
simplify
2+4+6+8+10+12+14
Then evaluate and you get 56


Now, expand
8
E 2i(^2)-1
i=5

2*5(^2)-1+2*6(^2)-1+2*7(^2)-1+2*8(^2)-1
In expanded form this ^ is 49+71+97+127

Simple enough, right?