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Discrete Math: Proofs

Use a form of Direct Proof to prove that any non-zero rational number can be written as the product of 2 irrational numbers. A partial proof has been given below.

1. Let 𝑛 be any non-zero rational number.
2. Then, 𝑛 can be written as √2 ( n / √2 )
3. √2 is an irrational number.
Reply 1
Original post by rick flick
Use a form of Direct Proof to prove that any non-zero rational number can be written as the product of 2 irrational numbers. A partial proof has been given below.

1. Let 𝑛 be any non-zero rational number.
2. Then, 𝑛 can be written as √2 ( n / √2 )
3. √2 is an irrational number.

So what are your thoughts on this? You've been given virtually all the pieces in the partial solution :smile:
Reply 2
Original post by davros
So what are your thoughts on this? You've been given virtually all the pieces in the partial solution :smile:

I know how to solve this by contradiction, but I'm not too sure how to go about using direct proofs.
I guess to start we need to prove that ( n / √2 ) is irrational as well, and that translates to a / b(√2 )
I'm not sure how to carry on from here
Reply 3
Original post by rick flick
I know how to solve this by contradiction, but I'm not too sure how to go about using direct proofs.
I guess to start we need to prove that ( n / √2 ) is irrational as well, and that translates to a / b(√2 )
I'm not sure how to carry on from here

Yes, if n is rational you basically want to produce 2 numbers u and v that multiply together to give n, and be able to show that both u and v are irrational.

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