.

You can make a right triangle.

The reason for this is the following：

4- 1=3

(fourth knot and first knot)

8-4=4 (fourth and eighth)

13-8=5 (8th and 13th)

Do △ABC

Let AB=5, BC=3 and AC=4.

BC? +AC？ =3? +4? =25

AB？ =5? =25

∴BC？ +AC？ =AB？

That is, △ABC is Rt△.

9.( 1)53

(2) Connect a diagonal line in a 2× 1 rectangle and make a square with its side length, with an area of 5.

Make a square with an area of 10 with a diagonal line in a rectangle with a side length of 3× 1.

A square with an area of 13 consists of a diagonal line in a 3×2 rectangle.