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# Hi! A new concept is being introduced and I'd like to figure out some of these examples with answers.

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Hi! A new concept is being introduced and I'd like to figure out some of these examples with answers.

1.

What is the sum of the series?

2.

what is the sum of this series?

3. What is the sum of the series?

Thank you all! :)

Apr 4, 2019

#1
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First one

First term  = 2(1)  = 2

Fifth term  = 2(5)  = 10

Sum of series  =

[ first term + last term ] *  number of terms  /  2    =

[ 2 + 10 ] * [ 5] / 2  =

12 * 5 / 2  =

60 / 2  =

30

Apr 4, 2019
#2
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Second one...not arithmetic or geometric......probably easiest to just list the terms

First term  ( 2 * 1)^2  =  4

Second term  = (2 * 2)^2  =  16

Thirs term = (2 * 3)^2  = 36

Fourth term  (2 * 4)^2 = 64

Sum  = 120

Apr 4, 2019
#3
+111432
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Last one

First term  =  -2(3) + 5  =  -1

Last term = -2(6) + 5 =  -7

Sum

[ first term + last term ] * number of terms  / 2  =

[ -1 + -7 ] *  4  / 2  =

-8 * 4  / 2  =

-16

Apr 4, 2019