Proof by Induction: Sum of 2^n - 1 Explained Step by Step

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Homework Help Overview

The discussion revolves around proving the formula for the sum of a geometric series, specifically the expression 1 + 2 + 2^2 + 2^3 + ... + 2^(n-1) = 2^n - 1, using mathematical induction. Participants are exploring the steps necessary for a proof by induction.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the necessity of establishing a base case and the inductive step for proving the statement. There is confusion regarding the term "similar bases" and how it relates to the proof. Some suggest alternative approaches, such as manipulating the sum directly.

Discussion Status

The conversation is ongoing, with participants clarifying the requirements of the induction proof. Some guidance has been provided regarding the steps needed, but there is no consensus on the interpretation of "similar bases" or the overall approach to the proof.

Contextual Notes

Participants are reminded of the forum's rules against providing complete solutions, which influences the nature of the discussion. There is an emphasis on understanding the proof structure rather than solving the problem outright.

Math325
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Homework Statement


1 + 2 + 2^2 + 2^3 + ...+2^(n-1) = 2^n - 1

Homework Equations


Sum formula?

3. The Attempt at a Solution

I know you are suppose to use the base case and prove its true for k +1, but I'm not sure what to do for similar bases. Can someone please solve it step by step? Thanks!
 
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Math325 said:

Homework Statement


1 + 2 + 2^2 + 2^3 + ...+2^(n-1) = 2^n - 1

Homework Equations


Sum formula?

3. The Attempt at a Solution

I know you are suppose to use the base case and prove its true for k +1, but I'm not sure what to do for similar bases. Can someone please solve it step by step? Thanks!
No, we won't "solve" it for you step by step. The Physics Forums rules expressly forbid this. Anyway, you're not "solving" this problem, you need to prove that the statement above is true for all integers n, n ≥ 1.

For an induction proof, you need to do three things.
1. Show that the statement is true for n = 1 or whatever the base case is. Do you know what statement you need to prove when n = 1?
2. Assume that the statement is true for n = k. What does this statement look like?
3. Show that the statement is true for n = k + 1. You will need to use the assumption of step 2 to do this.
 
If you don't have to use induction, you can let A = the sum, and see what 2A looks like. 2A-A=A.
 
I'm not sure what you mean by "similar bases". What similar bases are you referring to?

Math325 said:

Homework Statement


1 + 2 + 2^2 + 2^3 + ...+2^(n-1) = 2^n - 1
This says that 1= 2^1- 1= 2- 1, 1+ 2= 2^2- 1= 4- 1= 3 , 1+ 2+ 4= 2^3- 1= 8- 1= 7, etc.
The "base case" is, of course, when n= 1. Is "1= 2^1- 1" true?
Now, suppose 1+ 2+ 4+ 8+ ...+ 2^(n-1)= 2^n- 1. Write 1+ 2+ 4+ 8+ ...+ 2^(n-1)+ 2^n= (1+ 2+ 4+ 8+ ...+ 2^(n-1))+ 2^n

2. Homework Equations
Sum formula?

3. The Attempt at a Solution

I know you are suppose to use the base case and prove its true for k +1, but I'm not sure what to do for similar bases. Can someone please solve it step by step? Thanks!
 

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