Question

5. (6 points) Find the sum of the series represented by:
∑3 − 5 6 =1

Answer 1

-9

Explanation:

split the sequence to 3∑i - ∑5

the first is use formula

∑i = i*(i+1)/2

and ∑5 = 5i

subtract

6*7/2 - 5*6 = -9