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
