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istjohntoday at 2:15 PM4 repliesview on HN

Doesn't this allow one to prove x=y for any x, y?

x/0 = x(1/0) = x*0 = 0, so x/0 = 0 for all x.

So x/0 = y/0.

Multiply both sides by 0: x = y.


Replies

Smaug123today at 3:15 PM

What theorem did you use that allowed you to multiply both sides by $0$? (That theorem had conditions on it which you didn't satisfy.)

rnhmjojtoday at 2:32 PM

No, because x/y is just an arbitrary operation between x and y. Here you're assuming that 1/x is the inverse of x under *, but it's not.

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