1. Let's clarify the problem. You seem to be asking about proving an expression involving $2n$ and $n-1$. Please specify the exact statement or equation you want to prove. 2. Assuming you want to prove something like $2n = n - 1$, let's check if this equality holds. 3. Subtract $n$ from both sides: $$2n - n = n - 1 - n$$ which simplifies to $$n = -1$$ 4. This shows that $2n = n - 1$ only holds if $n = -1$. 5. If the problem is different, please provide more details for an accurate step-by-step proof.