The shortest distance between two points is a straight line. IF you draw a straight line from first to third you'll get a diagonal and cut the square into a right triangle. What's more its a special triangle ,which you should memorize, with the side proportions in which the legs are equal (a ) and the hypotenuse is a*square root 2
Since you know the legs here are 90 just multiply that by the square root of 2.
You should get the approximate answer of 127.3
