To distinguish between the statements provided:
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Statement #1: "All triangles have three sides and three angles."
- This is a definition of a triangle rather than a theorem. It describes the fundamental characteristics of triangles.
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Statement #2: "The interior angles of any triangle sum to 180 degrees."
- This is a theorem in geometry. It can be proven through various methods, such as through parallel lines or by using Euclidean geometry.
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Statement #3: "a + b = b + a"
- This is an example of the commutative property of addition. While it's a mathematical principle, it's more of a property than a theorem.
Therefore, Statement #2 is a theorem.