(12C Platinum) Geometric Progression

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ALG mode solution for Geometric Progression

a = First Term
r = Common Ratio
n = nth Term

S = a + ar + ... + ar^n-1

Where S = a(1-r^n) / 1-r
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Procedure:

a [R/S] r [R/S] n [R/S] display S
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Example:

Find the sum of the geometric series

8 - 4 + 2 - 1 + ...

where there are 5 terms in the series

8 [R/S] display 8.00
.5 [CHS] [R/S] display -0.50
5 [R/S] display 5.5

Answer: The 5 terms is 5.5
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Program: ALG mode

Quote:[STO] 0 [R/S]
[STO] 1 [Y^X] ( [R/S] [-] 1 ) [x] [RCL] 0 [=]
[x] [RCL] 1 [-] [RCL] 0 [÷] ( [RCL] 1 [-] 1 ) [=]

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