Question

Determine the sum of the first 20 terms of an arithmetic series with an

Answer 1

Answer:

440

Step-by-step explanation:

Determine the sum of the first 20 terms of an arithmetic series with an

initial term of 3 and a common difference of 2.

We have:

formula:   a_n = (n -1)d + a_1

SUM [from n= 1 to m]  a_n = SUM [n=1 to m] (n -1)d + a_1  = d* (m-1)*m/2  +  m*a_1  = m* (a_m + a_1)/2

a_20 = (20 -1)*2 + 3 = 19*2 + 3 = 38 + 3 = 41

a_1 = 3

so  SUM [n=1 to 20] = 20* (41 + 3)/2 = 20 * 44/2 = 10*44 = 440