A practical and beautiful tautology

Hello Rabbi,
As I understand it, a tautology is a sentence that is meaningless because it is always true. For example, the sentence x = x is meaningless because it is always true.
Although, for example, mathematical theorems, which are necessarily tautological (because they state x = x), can produce new content, such as practical applications. For example: Using the Pythagorean theorem, one can know whether the triangle in front of them is right-angled.
How is it possible that a tautological sentence devoid of content can create content?