i know how to prove that the product of two odd numbers is odd, but how would i go about proving the other direction... What if i needed to use this as an if and only if statement in a proof, thanks

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    $\begingroup$ Hint: Try proving the contrapositive. That is to say, if at least one of $a,b$ is even prove that $a\times b$ must also be even. Do you see why this is equivalent to showing that if $a\times b$ is odd then $a$ and $b$ are both odd? $\endgroup$ – JMoravitz Nov 8 '18 at 1:12
  • $\begingroup$ ok thanks i will try $\endgroup$ – Carlos Bacca Nov 8 '18 at 1:13

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