rove the following statement directly from the definition of rational number. The difference of any two rational numbers is a rational number. Proof: Suppose r and s are any two rational numbers. By definition of rational, r = a b and s = c d for some ---Select--- a, b, c, and d with ---Select--- . 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. r − s = Both the numerator and the denominator are integers because ---Select--- . In addition, bd ≠ 0 by the ---Select--- . Hence r − s is a ---Select--- of two integers with a nonzero denominator, and so by definition of rational, r − s is rational.