Note that there may be two solutions to this problem: two triangles with a circumference difference of 3cm, which may be that the circumference of the upper triangle minus the circumference of the lower triangle is 3cm, or that the circumference of the lower triangle minus the circumference of the upper triangle is 3cm.

Assuming that half of the waist length is x, then the waist length is 2x and the bottom length is 2 1-4x.

1, the perimeter of the upper triangle minus the perimeter of the lower triangle is 3cm,

3x-(2 1-4x+x)=3

6x=24

x=4，

So the three sides of the triangle are 8 cm, 8 cm and 5 cm respectively.

2. The perimeter of the lower triangle minus the perimeter of the upper triangle is 3cm.

(2 1-4x+x)- 3x=3

6x = 18

x=3

So the three sides of the triangle are 6 cm, 6 cm and 9 cm respectively.

To sum up, the three sides of a triangle are 6 cm, 6 cm, 9 cm or 8 cm, 8 cm and 5 cm respectively.