Let S be the statement: The cube root of every irrational number is irrational. This statement is true, but the following "proof" is incorrect. Ex- plain the mistake. "Proof (by contradiction): Suppose not. Suppose the cube root of every irrational number is rational. But 2√2 is irrational because it is a product of a rational and an irrational number, and the cube root of 2√2 is √2, which is irratio- nal. This is a contradiction, and hence it is not true that the cube root of every irrational number is rational. Thus the statement to be proved is true."
Let S be the statement: The cube root of every irrational number is irrational. This statement is true, but the following "proof" is incorrect. Ex- plain the mistake. "Proof (by contradiction): Suppose not. Suppose the cube root of every irrational number is rational. But 2√2 is irrational because it is a product of a rational and an irrational number, and the cube root of 2√2 is √2, which is irratio- nal. This is a contradiction, and hence it is not true that the cube root of every irrational number is rational. Thus the statement to be proved is true."
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Transcribed Image Text:5. Let S be the statement: The cube root of every
irrational number is irrational. This statement is
true, but the following "proof” is incorrect. Ex-
plain the mistake.
"Proof (by contradiction): Suppose not.
Suppose the cube root of every irrational number
is rational. But 2√2 is irrational because it is
a product of a rational and an irrational number,
and the cube root of 2√2 is √2, which is irratio-
nal. This is a contradiction, and hence it is not
true that the cube root of every irrational number
is rational. Thus the statement to be proved
is true."
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