Chapter 10 - Cumulative Review - Page 634: 49

$d=\sqrt{2}\text{ units}$

Using the Distance Formula, then the distance between $ (2,-5) \text{ and } (1,-4) $ is \begin{array}{l} d=\sqrt{(x_1-x_2)^2-=(y_1-y_2)^2} \\\\ d=\sqrt{(2-1)^2+(-5-(-4))^2} \\\\ d=\sqrt{1+1} \\\\ d=\sqrt{2}\text{ units} .\end{array}