# The perimeter of the rectangle is 28 cm, the length of one of its sides is 11 cm. Find the area of the rectangle.

1) Find the length of the second side of the rectangle, knowing the perimeter and one side. The perimeter of a rectangle is the sum of the length and width of the rectangle multiplied by 2. Let’s write the formula:

P = (a + b) × 2,

where a and b are the sides of the rectangle.

Suppose we are given side a, we express side b from the formula for the perimeter:

P = 2a + 2b,

2b = P-2a,

b = (P-2a): 2.

Substituting the values of the perimeter and side a into the formula, we find the side b:

b = (28-2 × 11): 2 = (28-22): 2 = 6: 2 = 3 cm.

2) Find the area of the rectangle.

The area of a rectangle is the product of the lengths of its sides. Let’s write the formula for the area:

S = a × b,

S = 11 × 3 = 33 cm².

Answer: the area of the rectangle is 33 cm².