### Home > PC > Chapter 6 > Lesson 6.3.1 > Problem6-115

6-115.

Rewrite each of the following series using summation notation.

1. $\cos \left(1.2\right) + \cos \left(1.5\right) + \cos \left(1.8\right) + … + \cos \left(3.9\right)$

$\displaystyle \sum _{k=0}^{\text{terms}-1}\text{cos(pattern)}$

2. $1 − 3 + 5 − 7 + 9 − 11 + … + 201$

What expression would change the sign back and forth ($+$ to $−$)?

$n$ is an integer.

What expression gives odd numbers?

$2n + 1$