Rewrite each of the following series using summation notation.  

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

   Hint (a):

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

   sequence $= 1.2, 1.5, 1.8, …$
   Write an expression for this sequence.

2. $1 − 3 + 5 − 7 + 9 − 11 + … + 201$ 

   Hint (b):

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

   Answer 1(b):

   $(−1)^n$
   $n$ is an integer

   More Help (b):

   What expression gives odd numbers?

   Answer 2(b):

   $2n + 1$