2-1

Could you clarify what you mean by "2-1"?

• If it's the arithmetic 2 − 1, the answer is 1.
• If you mean problem 2-1 from a textbook or exam, please share the exact prompt or topic (subject, e.g., Calculus 2.1, Linear Algebra 2.1, etc.) and the problem statement, and I’ll walk you through a solution.