"1+1" is a linear expression of the character "1" on the left then the character "+" to the right of it then the character "1" to the right of the second character. It has three characters, whereas the expression "2" is a single character. Just counting how many characters they have shows that they are different.
You can set up a mathematical system with an equality relation and say that the two expressions satisfy that relation but that doesn't mean that they are the same.
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