RATIONAL & IRRATIONAL NUMBERS, QUICK CHECK:

HOW DOES THE CLOSURE PROPERTY PROVE THAT THE SUM OF A RATIONAL AND IRRATIONAL NUMBER IS IRRATIONAL?
1. THE SUM OF AN IRRATIONAL NUMBER CAN'T BE PREDICTED.
2. THE SUM OR DIFFERENCE OF A RATIONAL AND IRRATIONAL NUMBER IS A RATIONAL NUMBER.
3. IRRATIONAL NUMBERS CAN BE ADDED OR SUBTRACTED.
4. THE SUM OR DIFFERENCE OF TWO RATIONAL NUMBERS IS RATIONAL NUMBER.

1 answer

To understand how the closure property can be used to prove that the sum of a rational number and an irrational number is irrational, let's analyze the options you provided:

  1. The sum of an irrational number can't be predicted.

    • This statement is vague and not directly related to the closure property. It does not contribute to understanding the relationship between rational and irrational numbers.
  2. The sum or difference of a rational and irrational number is a rational number.

    • This statement is incorrect. The closure property does not support this statement. In fact, it is known that the sum (or difference) of a rational number and an irrational number is always irrational.
  3. Irrational numbers can be added or subtracted.

    • While this statement is true, it does not specifically address the relationship between rational and irrational numbers with respect to their sum or difference.
  4. The sum or difference of two rational numbers is a rational number.

    • This statement is true and illustrates the closure property of rational numbers. However, it doesn't directly address the case of adding a rational number to an irrational number.

Conclusion:

To demonstrate that the sum of a rational number \( r \) and an irrational number \( i \) is irrational using the closure property, you would argue as follows:

  • Assume, for the sake of contradiction, that \( r + i \) is rational.
  • If \( r + i \) is rational, then we can represent it as \( r + i = q \) for some rational number \( q \).
  • This implies that \( i = q - r \).
  • Since the difference of two rational numbers (both \( q \) and \( r \) are rational) is rational, \( i \) would also be rational.
  • This contradicts the assumption that \( i \) is irrational.

Hence, the correct reasoning shows that the sum of a rational and an irrational number is indeed irrational based on the properties of rational and irrational numbers, especially considering the definition of what it means for a number to be rational or irrational.