Basic math proof by contradiction (1 Viewer)

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[SOLVED] basic math proof by contradiction

1. The problem statement, all variables and given/known data

prove: If a and b are positive numbers, a/b +b/a>=2

2. Relevant equations



3. The attempt at a solution

by contradiction (a^2+b^2)/ab<2 and got lost
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
 

Dick

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If (a^2+b^2)/ab<2 then a^2+b^2<2ab. So a^2+b^2-2ab<0. But a^2+b^2-2ab=(a-b)^2<0. What could be wrong with that?
 
thanks it was that easy
 

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