A Rectangle has 4 sides
and opposite sides of a Rectangle are equal.
Let AB = l & BC = b
So, CD = AB = l
& AD = BC = b
Thus,
Perimeter = Sum of all sides
= AB + BC + CD + AD
= l + b + l + b
= 2 l + 2b
= 2( l + b)
So we can write,
Perimeter of rectangle = 2( l + b)
where l is length and b is width of rectangle