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this is not proof, though. can you prove it in general?
Welcome to the forum.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.
You must be careful, but many proofs can be made by pictures alone. You must use caution because picture proofs can charm your intuition which can be easily fooled and furthermore, it is easy to ignore important conditions to your theorems!