If x is even, then 7x + 9 is odd.

Calculus: Early Transcendentals
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ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
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Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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Use direct proofs

**Mathematical Statement:**

If \( x \) is even, then \( 7x + 9 \) is odd.

**Explanation:**

This statement expresses a mathematical condition and conclusion:

- **Condition:** \( x \) is an even number.
- **Conclusion:** When \( 7 \times x \) (where \( x \) is even) is computed and 9 is added to the result, the final value is an odd number.

**Reasoning:**

To understand why this is true, consider the properties of even and odd numbers:

1. **Even Numbers:** Any even number can be expressed as \( 2k \), where \( k \) is an integer.
2. **Odd Numbers:** An odd number can be expressed as \( 2m + 1 \), where \( m \) is an integer.

When \( x \) is even, it can be written as \( x = 2k \). Substituting this into the equation \( 7x + 9 \), we get:

\[ 
7(2k) + 9 = 14k + 9 
\]

Breaking this down:

- \( 14k \) is an even number because it is 2 times an integer.
- Adding 9 (an odd number) to an even number results in an odd number.

Thus, \( 7x + 9 \) is confirmed to be odd when \( x \) is even.
Transcribed Image Text:**Mathematical Statement:** If \( x \) is even, then \( 7x + 9 \) is odd. **Explanation:** This statement expresses a mathematical condition and conclusion: - **Condition:** \( x \) is an even number. - **Conclusion:** When \( 7 \times x \) (where \( x \) is even) is computed and 9 is added to the result, the final value is an odd number. **Reasoning:** To understand why this is true, consider the properties of even and odd numbers: 1. **Even Numbers:** Any even number can be expressed as \( 2k \), where \( k \) is an integer. 2. **Odd Numbers:** An odd number can be expressed as \( 2m + 1 \), where \( m \) is an integer. When \( x \) is even, it can be written as \( x = 2k \). Substituting this into the equation \( 7x + 9 \), we get: \[ 7(2k) + 9 = 14k + 9 \] Breaking this down: - \( 14k \) is an even number because it is 2 times an integer. - Adding 9 (an odd number) to an even number results in an odd number. Thus, \( 7x + 9 \) is confirmed to be odd when \( x \) is even.
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