1. The problem asks how the fraction $-\frac{2}{1}$ occurred. 2. This fraction represents a negative number where the numerator is $-2$ and the denominator is $1$. 3. The fraction $-\frac{2}{1}$ simplifies to $-2$ because dividing by $1$ does not change the value. 4. In general, a fraction $\frac{a}{b}$ means $a$ divided by $b$, and if $a$ is negative, the whole fraction is negative. 5. So, $-\frac{2}{1}$ means $-2$ divided by $1$, which equals $-2$. 6. This fraction might have occurred from an operation like subtracting $2$ or multiplying by $-1$. 7. The key rule is that dividing by $1$ leaves the number unchanged, so the negative sign stays with the numerator. Final answer: $-\frac{2}{1} = -2$