Hello.
This is a classic example of proof by contradiction, although there are many more ways to prove this statement, of course.
To prove by contradiction, we will assume the opposite of the statement and prove that it is false, hence making our original statement true.
Firstly, we must consider the possible outcomes of this question, which are either: √2 is rational or √2 irrational. Since the statement requires us to prove that √2 is irrational, we will assume that √2 is rational, and prove that the assumption is false, hence only leaving the conclusion that √2 is in fact irrational.
Proof:
How to prove by contradiction that √2 is irrational?
I hope this was helpful.