## Precalculus (6th Edition) Blitzer

$\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$
RECALL: The distance $d$ between two points is given by the formula: $d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2},$ where $(x_1, y_1)$ and $(x_2, y_2)$ are the coordinates of the two points. Thus, the missing expression in the given statement is: $\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}.$