Which option is a wrong start in the proof of \(\sqrt{2}\)?

Correct answer: Assuming \(\sqrt{2}=\frac{m}{0}\)

To prove that \(\sqrt{2}\) is irrational by contradiction, we first assume it is rational and write \(\sqrt{2}=\frac{m}{n}\), where \(m,n\) are coprime and \(n\ne0\). The expression \(\frac{m}{0}\) is undefined, so option C is an invalid start. In option A, the denominator is non-zero, so it is a valid assumption. Exam tip: whenever a rational number is written as \(\frac{p}{q}\), check that \(q\ne0\).