i have the question 'prove that if a and b are coprime, then ab and a+b are also coprime.' i have no idea where to start.. ?

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- Oct 24th 2012, 05:20 AMalgebra123proof of coprime numbers
i have the question 'prove that if a and b are coprime, then ab and a+b are also coprime.' i have no idea where to start.. ?

- Oct 24th 2012, 05:28 AMemakarovRe: proof of coprime numbers
Hint: Use proof by contrapositive and express aČ and bČ as linear combinations of ab and a + b.