### Theory:

The perimeter of a rectangle: The perimeter is the total distance around the outside, which can be constructed by adding together the length and breadth of each side.

Let us consider a rectangle $$ABCD$$ of length $$l$$ units and breadth $$b$$ units. Therefore, the perimeter of the rectangle is as follows:
$$Perimeter (P) = (AB + BC + CD + DA)$$ units.
$$P = ( l + b + l + b )$$ units.
$$P = (2l + 2b)$$ units.
$$P = 2 (l + b)$$ units.
Thus, the length of perimeter $$l = P/2 - b$$ unit.
And, the breadth of perimeter $$b = P/2 - l$$ unit.
Area of rectangle: The area of a rectangle is given by multiplying the width times the height.

Let us consider a rectangle $$ABCD$$ of length $$l$$ units and breadth $$b$$ units. Therefore, the area of the rectangle is as follows:
$$Area (A) = length × breadth$$
$$A = l × b$$ square units.
Thus, the length of the rectangle $$l = A/b$$ unit.
And, the breadth of the rectangle $$b = A/l$$ unit.
Diagonals of rectangle: A rectangle has two diagonals they are equal in length and intersect in the middle. The diagonal is the square root of (width squared + height squared).

$$Diagonal (d) =$$ $\sqrt{{l}^{2}+{b}^{2}}$
Where $$l$$ is the length of the rectangle.
Where $$b$$ is the breadth of the rectangle.