You know the perimeter and one of its sides. How do you find the other side of the rectangle?

The perimeter of a rectangle is the sum of all its sides.

We introduce the designation:

A- one side of the rectangle.

B is the other side of the rectangle.

P is the perimeter of the rectangle.

Given that the opposite sides of the rectangle are equal, we find the perimeter:

P = 2A + 2B = 2 (A + B).

If you know the perimeter and one of the sides of the rectangle, say B, we find the side A from the formula:

2A = P – 2B;

A = (P – 2B) / 2.

Answer: A = (P – 2B) / 2.