The perimeter of the rectangle ABCD is 40cm, the side of AB is 8cm, find the area of the rectangle ABCD.

The first step is to find the length of the rectangle, knowing that the perimeter is 40 cm and the width is 8 cm. The perimeter of the rectangle is twice the sum of the length and width. Let’s denote the length by “x” cm.

(x + 8) * 2 = 40;

Find the value of the sum in parentheses, which is a factor. To do this, divide the product 40 by the second factor 2.

x + 8 = 40/2;

x + 8 = 20;

x = 20 – 8;

x = 12.

Let’s calculate what is equal to the area of a rectangle 12 cm long and 8 cm wide. The area of a rectangle is equal to the product of length and width.

S = 12 * 8 = 96 cm².

Answer: 96 cm².