Rewrite each of the following series using summation notation.

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

   Hint (a):

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

2. $1 − 3 + 5 − 7 + 9 − 11 + … + 201$

   Hint 1(b):

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

   Answer 1(b):

   $n$ is an integer.

   Hint 2(b):

   What expression gives odd numbers?

   Answer 2(b):

   $2n + 1$