Is the set of imaginary numbers closed under subtraction?

Yes, the set of imaginary numbers is closed under subtraction. This means that if you take any two imaginary numbers, their difference will also be an imaginary number. For example, subtracting ( bi ) from ( ai ) (where ( a ) and ( b ) are real numbers) results in ( (a - b)i ), which remains an imaginary number. Therefore, the set of imaginary numbers is closed under this operation.