2-1

Could you clarify what you mean by "2-1"? A couple of possibilities:

• If you’re asking for the arithmetic: 2 − 1 = 1.
• If you’re referring to problem 2-1 from a textbook (chapter 2, section 1) or a course problem: please paste the full problem statement or tell me the subject and course, and I’ll solve it step by step.

If you paste the problem, I’ll provide a clear solution, key concepts, and common pitfalls.