13-6

So, who else failed that Chapter test? HAHA. Looks like everyone needs another holiday already..
Section 6 of 13 was about sigmas. A sigma is a series written in condensed form. If you didn’t know, a series is a list of numbers being added together. This section was fairly easy if you knew the parts of the sigma.

EXAMPLE 1:
6
∑ 3k
k = 1

Limits of summation – 1, 6
Index – k
Summand – 3k

A). Expand the sigma.
3(1) + 3(2) + 3(3) + 3(4) + 3(5) + 3(6) + 3(7)
3 + 6 + 9 + 12 + 15 + 18 + 21

B). Evaluate the sigma.
3 + 6 + 9 + 12 + 15 + 18 + 21 = 78

EXAMPLE 2: Express using a sigma – 7 + 3 -1 -5 -9
5
∑ 11-4k
k = 1

*k=1 when working backwards!