△BCD is an isosceles right triangle, and the side length ratio is 1: 1: root number 2.

So BC=5, count 2 cm.

△ABC is a right triangle with an angle of 60 degrees, and the ratio of three sides is 1: the root sign is 3:2.

So AC = BC * 2/ root number 3 =10/3 * the square root of 6 cm.