Posted by Neil on Tuesday, May 29, 2012 at 8:40pm.
∑2n+7
=2∑n + ∑ 7
=2*(20+1)(20/2) + 20*7
=420+140
=560
Thank you, MathMate.
Wait, do you know how it could be plugged into the Sn= a1 (1 - r^n/ 1 - r) formula?
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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