11
YOUR ANSWER: The sentence is true.
You are correct. The sentence, or equation, 1+2 = 3 is true, at least in the mathematical sense that it is consistent with our definitions of the symbol 1, 2, and 3. Therefore, the statement 1+2 = 3 won't get us into any contradictions later on, which is all a mathematician, speaking as a mathematician, means by saying that a statement or equation is true.
Evidently we can write equations that are not true. For example, it is not true that
2 + 3 = 6
There is a special symbol that is used for saying that a particular mathematical sentence is not an equation. It is an equal sign with a slash through it
and is read "is not equal to" or "does not equal to". (Note: Since I have a hard time writing the above symbol, we will use the symbol !=, an exclamation point and an equal sign together, in place of the equal-sign-with-a-slash-through-it symbol.) The proper way to write our statement about 2, 3 and 6 above would be
2 + 3 != 6.
This would be read as "Two plus three is not equal to six." Consider the mathematical sentence
4 + 3 != 9.
Is this sentence true or false?