Writing a function that alternates plus and minus signs between list indices

Question

In a homework set I\'m working on, I\'ve come across the following question, which I am having trouble answering in a Python-3 function:

\"Write a fun

Answer 1

my_list = range(3, 20, 2)
sum(item * ((-1)**index) for index, item in enumerate(my_list))

sum = 11 (result of 3-5+7-9+11-13+15-17+19)