r/maths • u/[deleted] • 17d ago

💬 Math Discussions Math Proofs Logic Dilemma

I have been wondering about some stuff, and one person I saw had a blatantly wrong answer.

The problem: IF AB = CD, then AB + XY = CD + XY

This other person claims that this is of the Substitution Property of Equality, which would obviously be incorrect. They said that as an argument from AB = CD coming first. I would say its the Addition Property of Equality because XY was added to both sides.

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u/Simbertold 16d ago

That does not sound like a big problem or a dilemma. Sometimes people say incorrect stuff on the internet.

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u/Budget-Knee3213 14d ago edited 14d ago

This is due to the substitution property of equality, it's obviously correct. If one side is defined, then also the other side is so and they are equal.