Answer
$5$
Work Step by Step
The distance formula is: $d = \sqrt{(y_2-y_1)^2+(x_2-x_1)^2}$. This finds the distance $d$ between two points $(x_1,y_1)$ and $(x_2,y_2)$. Distances are always positive.
$d = \sqrt{(5-1)^2+(8-5)^2} = \sqrt{25} = 5$