Consider the following statement. 3√2-7 is irrational. This statement is true, but the following proposed proof by contradiction is incorrect. Proposed proof: Suppose not. That is, suppose 3√√2-7 is rational. By definition of rational, there exist real numbers a and b with a 3√2-7= and b + 0. b Using algebra to solve for √2 gives a + 7b 3b But a + 7b and 3b are real numbers and 3b + 0. 3b√/2 - 7b = a; and so √2 = Therefore, by definition of rational, √/2 is rational. This contradicts Theorem 4.7.1, which states that √2 is irrational. Hence the supposition is false. Identify the errors in the proposed proof. (Select all that apply.) ✔ There is an error in the algebra solving for √2. O For a proof by contradiction you should suppose that 3√/2 - 7 is irrational. To apply the definition of rational, a and b must be integers. ✔ The square root of 2 is rational, so there is no contradiction. ✔The statement to be proved is assumed. X

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question

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Consider the following statement.
3√2- - 7 is irrational.
This statement is true, but the following proposed proof by contradiction is incorrect.
Proposed proof:
Suppose not. That is, suppose 3√√√/2 - 7 is rational.
By definition of rational, there exist real numbers a and b with
a
3√2-7= and b + 0.
b
Using algebra to solve for V 2 gives
a + 7b
3b
But a + 7b and 3b are real numbers and 3b + 0.
3b√2 - 7b = a; and so 2 =
V
Therefore, by definition of rational, √2 is rational.
This contradicts Theorem 4.7.1, which states that
Hence the supposition is false.
2 is irrational.
Identify the errors in the proposed proof. (Select all that apply.)
✔There is an error in the algebra solving for ✓/2.
For a proof by contradiction you should suppose that 3√/2 - 7 is irrational.
To apply the definition of rational, a and b must be integers.
✔ The square root of 2 is rational, so there is no contradiction.
✔ The statement to be proved is assumed.
Transcribed Image Text:Consider the following statement. 3√2- - 7 is irrational. This statement is true, but the following proposed proof by contradiction is incorrect. Proposed proof: Suppose not. That is, suppose 3√√√/2 - 7 is rational. By definition of rational, there exist real numbers a and b with a 3√2-7= and b + 0. b Using algebra to solve for V 2 gives a + 7b 3b But a + 7b and 3b are real numbers and 3b + 0. 3b√2 - 7b = a; and so 2 = V Therefore, by definition of rational, √2 is rational. This contradicts Theorem 4.7.1, which states that Hence the supposition is false. 2 is irrational. Identify the errors in the proposed proof. (Select all that apply.) ✔There is an error in the algebra solving for ✓/2. For a proof by contradiction you should suppose that 3√/2 - 7 is irrational. To apply the definition of rational, a and b must be integers. ✔ The square root of 2 is rational, so there is no contradiction. ✔ The statement to be proved is assumed.
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