The perimeter of the rectangle is 40 cm and one of its old ones is 4 cm. Find the side of the square equal to the given rectangle.

In order to find the perimeter of a rectangle, you need to find the sum of all its sides or use the formula:

P = 2 * (a + b), where P is the perimeter of the rectangle, a is the width of the rectangle, and b is the length of the rectangle.

The perimeter and side of the rectangle are known, we find the second side:

a = P / 2 – b;

a = 40/2 – 4 = 20 – 4 = 16 (cm).

Equal area shapes are shapes that have the same area.

Find the area of ​​the rectangle:

S = a * b, where S is the area of ​​the rectangle;

S = 16 * 4 = 64 (cm ^ 2).

Find the side of the square, for this we use the formula for the area of ​​a square:

S = a ^ 2, a = √S = √64 = 8 (cm).

Answer: 8 cm.