Squareroot(x2-x1)^2+(y2-y1)^2
(4,5)(10,13)
=square root (13-5)^2+(10-4)^2
=square root 8^2+6^2
=square root 64+36
=square root 100
Rewrite it as
=square root 10^2
Pull terms out from under the radical, assuming positive real numbers.
=10
