Question

What is the sum of the first 20 terms of the series below?

Answer 1

the sum of the first 20 terms of the series below is C.

Answer 2

Explanation:

Now to find the sum of first 20 terms, substitute n=20,a=−1 and d=4 in S n = 2n [2a+ (n−1)d] as follows: S 20 = 220 [(2×−1)+(20−1)4]=10[−2+(19×4)]=10(−2+76)=10×74=740 Hence, the sum of first 20 terms is 740.