Thread is closed but answer has error

[rickhev]

I wanted to correct the answer to a thread, but it has been closed. What should I do? (The thread is https://www.physicsforums.com/threa...-2-the-square-root-of-2-is-irrational.270791/.)

 

[phinds]

I wanted to correct the answer to a thread, but it has been closed. What should I do? (The thread is https://www.physicsforums.com/threa...-2-the-square-root-of-2-is-irrational.270791/.)

Go to the thread and click "report" on the post you want to correct and type in a request to the mods to re-open the thread for you to do so.

 

[rickhev]

Go to the thread and click "report" on the post you want to correct and type in a request to the mods to re-open the thread for you to do so.

Thanks, I followed your suggestion.

 

[BobG]

You want to correct an error that was made seven years ago?

 

[rickhev]

You want to correct an error that was made seven years ago?

Why not?

 

[mfb]

Try to find the error.

;)

 

[rickhev]

Try to find the error.

;)

What do you mean? I've already found it.

 

[mfb]

Try to find it in the old thread. I found one and fixed it - was just a typo I guess.

 

[rickhev]

Try to find it in the old thread. I found one and fixed it - was just a typo I guess.

Thanks, it's mostly fixed. The phrase 'irrational multiplied by a rational' should also be changed to 'irrational multiplied by a non-zero rational'. Would you please make that change too?

 

[berkeman]

Thanks, it's mostly fixed. The phrase 'irrational multiplied by a rational' should also be changed to 'irrational multiplied by a non-zero rational'. Would you please make that change too?

I made the change, and added some whitespace to make it more readable. Does this look right now?

I figured it out. Posting solution in case sombody might run into the same problem in the future :P

I assume 2^(1/3) + 2^(1/2) = a , where a is rational

=> 2=(a-2^(1/2))^3 <=> 2 = (a^3 + 6a) + sqrt(2)(-3a^2 -2)

Which is a contradiction since sqrt(2)(-3a^2 -2) is an irrational multiplied by a non-zero rational, which can be proved to always be irrational, and the sum of a rational (a^3 + 6a) and an irrational can be proved to always be irrational, and above cannot equal 2 since 2 is rational.

 

[rickhev]

I made the change, and added some whitespace to make it more readable. Does this look right now?

Looks good to me. Thanks very much.