Problem 3 Use Mathematical Induction to prove that 1² + 3² + 5²+...+ (2n + 1)² = (n + 1)(2n + 1) (2n + 3) 3 whenever n is a nonnegative integer. Solution 2

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### Mathematical Induction Proof of Sum of Squares Formula

#### Problem 3
**Use Mathematical Induction to prove that**

\[ 1^2 + 3^2 + 5^2 + \cdots + (2n + 1)^2 = \frac{(n + 1)(2n + 1)(2n + 3)}{3} \]

**whenever \( n \) is a nonnegative integer.**

#### Solution:
\[
\begin{aligned}
& \text{Base case: Let } n = 0 \\
& (2 \cdot 0 + 1)^2 = \frac{(0 + 1)(2 \cdot 0 + 1)(2 \cdot 0 + 3)}{3} \\
& 1^2 = \frac{(1)(1)(3)}{3} \\
& 1 = 1 \text{, which is true.}
\end{aligned}
\]

Next step is to assume the statement is true for some \( k \) and then prove it for \( k+1 \). This will be the inductive step. 

\[
\text{Assume } \sum_{i=0}^k (2i + 1)^2 = \frac{(k + 1)(2k + 1)(2k + 3)}{3}
\]

Then we need to show:

\[
\sum_{i=0}^{k+1} (2i + 1)^2 = \frac{(k + 2)(2(k + 1) + 1)(2(k + 1) + 3)}{3}
\]

Add the next term \( (2(k+1) + 1)^2 \) to both sides of the assumed statement and simplify.

Completing the details of the induction step ultimately demonstrates that the formula works for \( k+1 \), and by induction, it holds for all nonnegative integers \( n \).

Thus, we have used mathematical induction to prove the given formula.
Transcribed Image Text:### Mathematical Induction Proof of Sum of Squares Formula #### Problem 3 **Use Mathematical Induction to prove that** \[ 1^2 + 3^2 + 5^2 + \cdots + (2n + 1)^2 = \frac{(n + 1)(2n + 1)(2n + 3)}{3} \] **whenever \( n \) is a nonnegative integer.** #### Solution: \[ \begin{aligned} & \text{Base case: Let } n = 0 \\ & (2 \cdot 0 + 1)^2 = \frac{(0 + 1)(2 \cdot 0 + 1)(2 \cdot 0 + 3)}{3} \\ & 1^2 = \frac{(1)(1)(3)}{3} \\ & 1 = 1 \text{, which is true.} \end{aligned} \] Next step is to assume the statement is true for some \( k \) and then prove it for \( k+1 \). This will be the inductive step. \[ \text{Assume } \sum_{i=0}^k (2i + 1)^2 = \frac{(k + 1)(2k + 1)(2k + 3)}{3} \] Then we need to show: \[ \sum_{i=0}^{k+1} (2i + 1)^2 = \frac{(k + 2)(2(k + 1) + 1)(2(k + 1) + 3)}{3} \] Add the next term \( (2(k+1) + 1)^2 \) to both sides of the assumed statement and simplify. Completing the details of the induction step ultimately demonstrates that the formula works for \( k+1 \), and by induction, it holds for all nonnegative integers \( n \). Thus, we have used mathematical induction to prove the given formula.
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