Let , and be lengths of sides of triangle . Prove that at least one of the equations does not have real solutions
Solution
1. Assume that each of the equations has at least one real solution.
For a quadratic equation to have real solutions, its discriminant must be nonnegative. The discriminant of the quadratic equation is given by:
For this equation to have real solutions, we must have:
2. Apply the same reasoning to the other two equations:
For the equation , the discriminant is:
For this equation to have real solutions, we must have:
For the equation , the discriminant is:
For this equation to have real solutions, we must have:
3. Add the inequalities obtained:
Adding these three inequalities, we get:
4. Compare with the triangle inequality:
The triangle inequality states that the sum of the lengths of any two sides of a triangle must be greater than the length of the remaining side. This implies:
Squaring these inequalities and adding them, we get:
Simplifying, we get:
5. Derive the contradiction:
From the inequalities derived from the discriminants, we have:
But from the triangle inequality, we have:
This is a contradiction. Therefore, our initial assumption that each of the equations has at least one real solution must be false.