Use induction to prove that Σmn1(2j + 1) = 3η2 3n²

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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### Proof by Mathematical Induction

We are given the following statement to prove using induction:

\[
\sum_{j=n}^{2n-1} (2j + 1) = 3n^2
\]

#### Step 1: Base Case
First, we need to verify the base case where \( n = 1 \).

When \( n = 1 \):
\[
\sum_{j=1}^{2 \cdot 1 - 1} (2j + 1) = 2 \cdot 1 + 1 = 3
\]
And:
\[
3 \cdot 1^2 = 3
\]
Thus, the base case holds true:
\[
\sum_{j=1}^{1} (2j + 1) = 3 = 3 \cdot 1^2
\]

#### Step 2: Inductive Hypothesis
Assume that for some integer \( k \geq 1 \), the statement holds true:
\[
\sum_{j=k}^{2k-1} (2j + 1) = 3k^2
\]

#### Step 3: Inductive Step
Prove that if the statement holds for \( n = k \), it must also hold for \( n = k+1 \).

Consider:
\[
\sum_{j=k+1}^{2(k+1)-1} (2j + 1)
\]

Expressing the sum:
\[
\sum_{j=k+1}^{2(k+1)-1} (2j + 1) = \sum_{j=k+1}^{2k+1} (2j + 1)
\]

Break it into two parts:
\[
\left( \sum_{j=k}^{2k-1} (2j + 1) \right) + (2(2k) + 1) + (2(2k+1) + 1)
\]

Using the inductive hypothesis, replace the sum up to \( 2k-1 \):
\[
3k^2 + (4k + 1) + (4k + 3)
\]

Simplifying the sum:
\[
3k^2 + 4k + 1 + 4k + 3 = 3k^2 + 8k + 4
\]
Transcribed Image Text:### Proof by Mathematical Induction We are given the following statement to prove using induction: \[ \sum_{j=n}^{2n-1} (2j + 1) = 3n^2 \] #### Step 1: Base Case First, we need to verify the base case where \( n = 1 \). When \( n = 1 \): \[ \sum_{j=1}^{2 \cdot 1 - 1} (2j + 1) = 2 \cdot 1 + 1 = 3 \] And: \[ 3 \cdot 1^2 = 3 \] Thus, the base case holds true: \[ \sum_{j=1}^{1} (2j + 1) = 3 = 3 \cdot 1^2 \] #### Step 2: Inductive Hypothesis Assume that for some integer \( k \geq 1 \), the statement holds true: \[ \sum_{j=k}^{2k-1} (2j + 1) = 3k^2 \] #### Step 3: Inductive Step Prove that if the statement holds for \( n = k \), it must also hold for \( n = k+1 \). Consider: \[ \sum_{j=k+1}^{2(k+1)-1} (2j + 1) \] Expressing the sum: \[ \sum_{j=k+1}^{2(k+1)-1} (2j + 1) = \sum_{j=k+1}^{2k+1} (2j + 1) \] Break it into two parts: \[ \left( \sum_{j=k}^{2k-1} (2j + 1) \right) + (2(2k) + 1) + (2(2k+1) + 1) \] Using the inductive hypothesis, replace the sum up to \( 2k-1 \): \[ 3k^2 + (4k + 1) + (4k + 3) \] Simplifying the sum: \[ 3k^2 + 4k + 1 + 4k + 3 = 3k^2 + 8k + 4 \]
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