This was taught by my teacher when I was in middle school. Now there are no books: P

If the solution is an empty set, there is no solution. Specifically, you can say that the solution is an empty set in real number field or complex number field. . . Different numeric fields have different meanings for the solution as an empty set. When you say that the solution in the real number field is an empty set, it doesn't necessarily mean that there is no solution in the complex number field. Anyway, you have to give a range first.

I later studied engineering in college, so I didn't forget these math things-