If , , and are rational numbers and the equation holds, prove that .
Problem 245
Official solution
Let's suppose that at least one of , , or is not equal to . We will check each assumption to see if the equation holds:
1. If and , the equation becomes . Since is not , must be to satisfy the equation, which is contradictory to the assumption.
2. If and , the equation becomes . This implies . Since and are rational numbers, and the square root of a non-square integer is an irrational number, is irrational. Therefore, the product of (a rational number) and (an irrational number) cannot equal (a rational number). This leads to a contradiction.
In both cases, we arrive at a contradiction, and therefore, , , and must all be equal to to satisfy the equation.