An example of an existence theorem that doesn't rely on constructive methods is the Intermediate Value Theorem (IVT) in real analysis. It states that if a continuous function $f$ takes values of opposite signs at two points, then there exists at least one point between them where the function equals zero. However, the proof of the IVT does not provide a specific method for finding that point, making it non-constructive.

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Here are 5 related questions:

1. What is the formal statement of the Intermediate Value Theorem?
2. Can you explain the difference between constructive and non-constructive proofs?
3. How do constructive methods approach existence theorems?
4. Are there specific examples of constructive versions of classical theorems?
5. What role do non-constructive methods play in functional analysis?

Tip: Non-constructive proofs often rely on indirect arguments like the law of excluded middle or the axiom of choice.