## Algebra 1: Common Core (15th Edition)

The slope equation is $\frac{y_{2}-y_{1}}{x_{2}-x_{1}}$. When you plug in 2 for $y_{2}$ and 1 in for $y_{1}$, you get 1. When you plug in 2 for $y_{2}$ and 3 in for $y_{1}$, you get -1. So, the fraction would be $\frac{1}{-1}$ which equals -1.