To clarify the proof that \( \frac{ad + bc}{bd} \) is a rational number, let's analyze it step by step.
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Understanding the elements: We are given that \( a, b, c, \) and \( d \) are integers, where \( b \) and \( d \) are non-zero. The expression in question is \( \frac{ad + bc}{bd} \).
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Calculate the numerator:
- The numerator is \( ad + bc \).
- Here, \( ad \) (the product of two integers) is an integer, and \( bc \) (the product of two integers) is also an integer.
- The sum \( ad + bc \) is therefore an integer, based on the Closure Property of integers, which states that the sum or product of two integers is an integer.
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Calculate the denominator:
- The denominator is \( bd \). Since both \( b \) and \( d \) are non-zero integers, \( bd \) is also a non-zero integer.
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Form the quotient:
- Now we examine the fraction \( \frac{ad + bc}{bd} \).
- The numerator \( ad + bc \) is an integer, and the denominator \( bd \) is a non-zero integer. Therefore, \( \frac{ad + bc}{bd} \) is a quotient of two integers.
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Conclusion:
- According to the definition of rational numbers, a rational number is any number that can be expressed as the quotient \( \frac{p}{q} \), where \( p \) and \( q \) are integers and \( q \neq 0 \).
- Since \( ad + bc \) is an integer and \( bd \) is a non-zero integer, \( \frac{ad + bc}{bd} \) is a rational number.
Thus, we can conclude that \( \frac{ad + bc}{bd} \) is indeed a rational number following the outlined steps based on the Closure Property. The key here is that both parts of the fraction (numerator and denominator) fulfill the criteria for forming a rational number.