Prove that for all integers n, n² – n + 3 is odd.

Advanced Engineering Mathematics
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**Mathematical Proofs and Concepts**

**1. Proof that for all integers \( n \), \( n^2 - n + 3 \) is odd.**

To prove that \( n^2 - n + 3 \) is odd for all integers \( n \), we need to consider the expression modulo 2. 

- **Case 1: \( n \) is even**  
  Let \( n = 2k \) for some integer \( k \).  
  Then \( n^2 = (2k)^2 = 4k^2 \), and \( n^2 - n + 3 = 4k^2 - 2k + 3 \).  
  Modulo 2, this simplifies to:  
  \[ 4k^2 \equiv 0 \pmod{2}, \quad 2k \equiv 0 \pmod{2}, \quad 3 \equiv 1 \pmod{2} \]  
  \[ n^2 - n + 3 \equiv 0 - 0 + 1 \equiv 1 \pmod{2} \]  
  Thus, \( n^2 - n + 3 \) is odd.

- **Case 2: \( n \) is odd**  
  Let \( n = 2k + 1 \) for some integer \( k \).  
  Then \( n^2 = (2k + 1)^2 = 4k^2 + 4k + 1 \), and \( n^2 - n + 3 = 4k^2 + 4k + 1 - (2k + 1) + 3 \).  
  Modulo 2, this simplifies to:  
  \[ 4k^2 \equiv 0 \pmod{2}, \quad 4k \equiv 0 \pmod{2}, \quad 1 - 1 + 3 \equiv 3 \equiv 1 \pmod{2} \]  
  \[ n^2 - n + 3 \equiv 0 + 0 + 1 \equiv 1 \pmod{2} \]  
  Thus, \( n^2 - n + 3 \) is odd.

In both cases, \(
Transcribed Image Text:**Mathematical Proofs and Concepts** **1. Proof that for all integers \( n \), \( n^2 - n + 3 \) is odd.** To prove that \( n^2 - n + 3 \) is odd for all integers \( n \), we need to consider the expression modulo 2. - **Case 1: \( n \) is even** Let \( n = 2k \) for some integer \( k \). Then \( n^2 = (2k)^2 = 4k^2 \), and \( n^2 - n + 3 = 4k^2 - 2k + 3 \). Modulo 2, this simplifies to: \[ 4k^2 \equiv 0 \pmod{2}, \quad 2k \equiv 0 \pmod{2}, \quad 3 \equiv 1 \pmod{2} \] \[ n^2 - n + 3 \equiv 0 - 0 + 1 \equiv 1 \pmod{2} \] Thus, \( n^2 - n + 3 \) is odd. - **Case 2: \( n \) is odd** Let \( n = 2k + 1 \) for some integer \( k \). Then \( n^2 = (2k + 1)^2 = 4k^2 + 4k + 1 \), and \( n^2 - n + 3 = 4k^2 + 4k + 1 - (2k + 1) + 3 \). Modulo 2, this simplifies to: \[ 4k^2 \equiv 0 \pmod{2}, \quad 4k \equiv 0 \pmod{2}, \quad 1 - 1 + 3 \equiv 3 \equiv 1 \pmod{2} \] \[ n^2 - n + 3 \equiv 0 + 0 + 1 \equiv 1 \pmod{2} \] Thus, \( n^2 - n + 3 \) is odd. In both cases, \(
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