Question

What is the sum of the finite arithmetic series?

(–5) + 0 + 5 + 10 + ... + 65

Answer 1

use the formula :
Sn = n/2 (a1 + an)

Answer 2

i kinda dont understand how to use it

Answer 3

but u have to find n, first

Answer 4

can you show me how i would do that ?

Answer 5

well, from the formula an = a1 + (n-1)d
with a1 = the first term and d=difference
given : an = 65, a1=-5, and its difference = 5 so
a1 + (n-1)d = 65
-5 + (n-1)5 = 65
-5 + 5n - 5 = 65
5n - 10 = 65
5n = 65 + 10
5n = 75
n = 75/5 = 15

Answer 6

it just get the n
now, we can determine the sum of that series :
Sn = n/2 (a1 + an)
plug the values of n=15, a1=-5, an=65 to formula above
S15 = 15/2 (-5 + 65)
S15 = 15/2 (60)
S15 = ...

Answer 7

450?

Answer 8

yes, that;s correct

Answer 9

yayy thank youu soo much!! :)

Answer 10

you're welcome