Posted by **Neil** on Tuesday, May 29, 2012 at 8:40pm.

20

(Sigma Sign) 2n + 7

k= 1

- Math -
**MathMate**, Tuesday, May 29, 2012 at 8:51pm
∑2n+7

=2∑n + ∑ 7

=2*(20+1)(20/2) + 20*7

=420+140

=560

- Math -
**Neil**, Tuesday, May 29, 2012 at 8:53pm
Thank you, MathMate.

- Math -
**Neil**, Tuesday, May 29, 2012 at 8:59pm
Wait, do you know how it could be plugged into the Sn= a1 (1 - r^n/ 1 - r) formula?

- Math -
**MathMate**, Tuesday, May 29, 2012 at 10:22pm
Sn= a1 (1 - r^n/ 1 - r)

applies when the series is a geometric progression, such as

20

∑ a1*r^i

i=1

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