Prove by dirrect or contrapositive method if a and b a real

Prove by dirrect or contrapositive method.....

if a and b a real numbers such that the product ab is an irrational number, then either a or b must be an irrational number

Solution

Proof by contrapositive method:

Assume it is not the case that either a or b is irrational. Then a and b are both rational. That implies ab is rational, which means not irrational. proof by contraposition.