CPM Homework Help : PC Problem 6-115

Hint (a):

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

Hint 1(b):

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

Answer (b):

(−1)ⁿ
n is an integer.

Hint 2(b):

What expression gives odd numbers?

Answer (b):

2n + 1