Find the length of the side of an equilateral triangle, the perimeter of which is equal

Find the length of the side of an equilateral triangle, the perimeter of which is equal to the perimeter of a rectangle with sides of 5 cm and 1 cm.

1. Determine the perimeter of the rectangle. The sum of the lengths of its sides is:
5 cm + 1 cm + 5 cm + 1 cm = 12 cm.

2. Since the triangle is equilateral by the condition of the problem, its perimeter is 3 * A, where A is the length of the side of the triangle.

3. By the statement of the problem, the perimeter of the triangle is equal to the perimeter of the rectangle. I.e,
3 * A = 12. Hence A = 12/3 = 4 cm.

Answer: the length of the side of the triangle is 4 cm.