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Discrete Mathematics and its Applications
Found in: Page 187
Discrete Mathematics and its Applications

Discrete Mathematics and its Applications

Book edition 7th
Author(s) Kenneth H. Rosen
Pages 808 pages
ISBN 9780073383095

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Short Answer

What is the sum of the terms of the geometric progression a+ar+...+arn when r1.

The sum of the terms of the geometric progression is Sn=a1-rn+11-r

See the step by step solution

Step by Step Solution

Step 1: Geometric progression

Given:

Sn=a+ar+...+arn with r1

Step 2: Finding sum of geometric progression

Let us determine rSn:

rSn=ar+ar2+...+arn+1

Next, we determine the difference between Sn and rSn

SnrSn=a+ar++arnar+ar2++arn+1=a+ar++arnarar2arn+1=aarn+1

Let us next use the distributive property on the obtained equality

Sn-rSn=a-arn+1Sn(1-r)=a(1-rn+1)

Divide each side by 1-r

Sn=a1-rn+11-r

Thus, the sum of the terms of the geometric progression is a1-rn+!1-r

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