what kind of math does economy use
The serious objections are, I think, two. (1.) The kind of mathematics used in economics is typically that of the Department of Mathematics, not that of the departments of Physics or of Engineering. It is existence-theorem, qualitative athematics. It is of no use for science. (2.) The kind of statistics used in economics is that of Department of Statistics, which is also a species of existence theorems.. Tests of statistical significance claim to tell whether there exists an effect of interest rates on investment. But this, too, is of no use for science.