## Geometry: Common Core (15th Edition)

$d_{AB}=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$ substitute given values $d_{AB}=\sqrt{(-3-1)^2+(-1-7)^2}$ simplify in parentheses $d_{AB}=\sqrt{(-4)^2+(-8)^2}$ simplify $d_{AB}=\sqrt{16+64}$ $d_{AB}=\sqrt{80}$