Lace needs to surround the edge of the square tablecloth, so the length of lace is exactly the circumference of the square tablecloth. So we need to calculate the circumference of the square tablecloth and then calculate the required lace length according to the circumference. It is known that the side length of a square tablecloth is 15 decimeter. We convert 15 decimeter into meter, and 15 decimeter equals 1.5 meter. According to the nature of a square, a square has four equal sides, so the circumference of a square is equal to four times the length of the side. Therefore, the circumference of a square tablecloth is: 1.5× 4 = 6m.

We need to calculate the required lace length according to the circumference. Since lace needs to surround the edge of the square tablecloth, the length of lace is equal to the circumference of the square tablecloth. The required lace length is: 6 meters. Therefore, it takes 6 meters of lace to sew a circle of lace on a square tablecloth with a side length of 15 decimeter.

Importance of square perimeter:

1, mathematics education

The perimeter of a square is a very important concept in mathematics education. It is the basis for students to master the general concept of polygon perimeter. By calculating the perimeter of a square, students can understand the definition of perimeter and how to calculate the perimeter by measuring the side length. This is helpful to cultivate students' geometric thinking and measurement skills.

2. Computer graphics images

In computer graphics, a square is a basic shape. When making animation, games or graphic design, it is often necessary to use squares to create backgrounds, interfaces or other elements. Calculating the perimeter of a square can help designers to determine the size and position of the square, so as to accurately build a graph.

3. Geometry and physics

In geometry and physics, a square is a shape with special properties. Its four sides are equal and all the angles are right angles. This symmetry makes squares have applications in many fields, including architectural design, crystal structure, circuit board design and so on. Calculating the circumference of a square can help to study the problems in these fields and verify the correctness of geometric and physical theories.