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tmua.fyi Paper 2 Challenge 2 · Q19

Paper 2Logic & proof

For positive real aa and bb, which single fact is enough to prove that ab+ba≥2\frac ab+\frac ba\ge2?

A(a−b)2≥0(a-b)^2\ge0
B(a+b)2≥0(a+b)^2\ge0
Ca2+b2≥0a^2+b^2\ge0
Dab>0ab>0
Eab>0 and ba>0\frac ab>0\text{ and }\frac ba>0
Fa>0 and b>0a>0\text{ and }b>0
Ga2+b2>aba^2+b^2>ab
H(a−b)2>0(a-b)^2>0

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