Question
find the sum of the arithmetic series 13+11+9+...+(-25)
Answers
Steve
clearly,
a = 13
d = -2
-25 = 13+19(-2), so -25 is A20
S20 = 20/2(13-25) = -120
a = 13
d = -2
-25 = 13+19(-2), so -25 is A20
S20 = 20/2(13-25) = -120
Find the sum of the terms in the arithmetic sequence
13+12+11+...20terms