Recent content by Uljanov

Thx, but I can't see how to proceed in the same manner. If xy=m/n, then x=m/(n*y), but if y is irrational I am back to the start, and can't say anything about x. In contradiction I assumed xy=m/n, and got y=m/(n*x)=ml/nk=m'/n' (x was rational), and this lead to the contradiction of y beeing...

Could you tell me how to write a very formal proof of the statement below with the contrapositive methode, if possible. (I know how to do it with contradiction) Let x be a rational number and y an irrational number, then x times y is irrational. V. Uljanov