Question

Find the designated sum of the arithmetic series.

S9 of 22+20+18+16+…

Answer 1

126

Explanation:

a = 22

d = 22- 20 = -2

n = 9

Sn = 0.5n(2a +d(n-1))

=0.5 * 9 (2 *22 +-2(9-1))

= 126