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tmua.fyi Mock Paper 2 (2) · Q5

Paper 2Logic & proof

To prove that 2\sqrt2 is irrational, a student writes 2=pq\sqrt2=\frac pq in lowest terms and correctly deduces that pp and qq are both even. What makes this a valid proof?

AIt contradicts the assumption that pq\frac pq is in lowest terms, so that assumption must be false.
BIt shows that 2\sqrt2 is an even number.
CIt proves that pp and qq do not exist.
DEven numbers cannot be written as a fraction.
EThe argument is not actually valid.

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