The formula of a distance between two points:
[tex]d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}[/tex]
We have the points (-1, 8) and (5, -2). Substitute:
[tex]d=\sqrt{(5-(-1))^2+(-2-8)^2}=\sqrt{6^2+(-10)^2}=\sqrt{36+100}=\sqrt{136}\\\\=\sqrt{4\cdot34}=\sqrt4\cdot\sqrt{34}=\boxed{2\sqrt{34}}[/tex]
