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A student assumes \(\sqrt{2}=p/q\), where \(p\) and \(q\) are coprime integers, to prove that \(\sqrt{2}\) is irrational. From \(p^2=2q^2\), the student writes \(p=2m\) and obtains \(q^2=2m^2\). The student says that since \(p\) and \(q\) are coprime, \(q\) must be odd. What is the correct correction to this statement?

Answer and explanation

Correct answer: \(q\) is even; therefore, both \(p\) and \(q\) are even, contradicting their coprimality.

The equation \(q^2=2m^2\) makes \(q^2\) even, so \(q\) must be even. Since \(p\) was already even, both share factor 2, contradicting coprimality. Exam tip: if a square is even, its integer root is even.

Related tags

Number SystemsIrrational NumbersProof By ContradictionSquare Root 2Coprime IntegersParityProof Of Irrationality Of Square Root 2 And Square Root 3Mathematics

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