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tmua.me Medium Set A Paper 2 · Q2

Paper 2Logic & proof

Consider the following claim about nonzero real numbers aa and bb:

If a<b, then 1a>1b.\text{If }a<b,\text{ then }\frac1a>\frac1b.

Which of the following is a counterexample to this claim?

Aa=1,b=3a=1,\quad b=3
Ba=−4,b=−2a=-4,\quad b=-2
Ca=2,b=−1a=2,\quad b=-1
Da=−1,b=−3a=-1,\quad b=-3
Ea=−2,b=3a=-2,\quad b=3

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