Text: DISCRETE MATH
Prove the following statement directly from the definition of a rational number.
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integers. The difference of any two rational numbers is a rational number. complex numbers negative numbers.
Proof: Suppose r and s are any two rational numbers. By the definition of rational, r = a/b and s = c/d for some real numbers a, b, c, and d with b and d being positive numbers.
Write r - s in terms of a, b, c, and d as a quotient of two integers whose numerator and denominator are simplified as much as possible. The result is the following:
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products and quotients of integers are rational numbers. Both the numerator and the denominator are integers because products and differences of integers are integers.
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products and quotients of rational numbers are integers. In addition, bd ≠0 by the zero product property.
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Hence, r - s is a product, sum, difference, or quotient of two integers with a nonzero denominator, and so by the definition of rational, r - s is rational.