### Theory:

The perimeter of a rectangle: The perimeter is the total distance around the outside, that can be created by adding together the length and the breadth of each side. Let us consider a rectangle $$ABCD$$ of  length '$$l$$' units and breadth '$$b$$' units.

The perimeter of the rectangle is therefore 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 the rectangle given its perimeter is $$l = P/2 - b$$ units.

And, the breadth of the rectangle given its perimeter is $$b = P/2 - l$$ units.
Area of rectangle: The area of a rectangle is given by multiplying the length and the breadth. 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 $$l$$ $$×$$ breadth $$b$$.

Thus, the length of the rectangle given its area is $$l = A/b$$ units.

And, the breadth of the rectangle given its area is $$b = A/l$$ units.
Diagonals f rectangle: A rectangle has two diagonals they are equal in length and intersect in the middle. The diagonal is the square root of (length squared + breadth squared). Diagonal $$(d) =$$ $\sqrt{{l}^{2}+{b}^{2}}$.

Where '$$l$$' and '$$b$$' is the length and breadth of the rectangle.