.
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.