The formula of a distance between two points:
[tex]d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}[/tex]
We have:
[tex](5,\ 6)\to x_1=5,\ y_1=6\\(-4,\ -7)\to x_2=-4,\ y_2=-7[/tex]
substitute:
[tex]d=\sqrt{(-4-5)^2+(-7-6)^2}=\sqrt{(-9)^2+(-13)^2}=\sqrt{81+169}=\sqrt{250}\\\\=\sqrt{25\cdot10}=\sqrt{25}\cdot\sqrt{10}=5\sqrt{10}[/tex]
