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Question:

Establish the existence of two irrational numbers A and B, such that the number AB is rational, or prove that such numbers do not exist.

 

Answer:

Let X = sqr(2)sqr(2), and B = sqr(2).
Either X is irrational; then, A = X, and AB = [ sqr(2)sqr(2) ] sqr(2) = 2 is rational.
Or X is rational; then A = B, and AB = X.

 

Tip:
  • Always read the problem clearly before you do it.