We know that 24=42 and (−2)−4=(−4)−2. Is there another pair of integers x,y (x≠y) which satisfies the equality xy=yx?

**Answer**

This is a classic (and well known problem).

The general solution of xy=yx is given by

x=(1+1/u)uy=(1+1/u)u+1

It can be shown that if x and y are rational, then u must be an integer.

**Attribution***Source : Link , Question Author : Paulo Argolo , Answer Author : J. M. ain’t a mathematician*