Area, perimeter and diagonals — lesson. Mathematics CBSE, Class 7.

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

Let us consider a rectangle of length

$l$ units and breadth

$b$ units. Therefore, perimeter of the rectangle

$ABCD$ .

$Perimeter$

$P =$

$(AB + BC + CD + DA)$ 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 of length

$l$ units and breadth

$b$ units. Therefore, area of the rectangle

$ABCD$ .

$Area$

$A=$

$length × breadth$

$A =$

$l × b$ 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.

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2. Area, perimeter and diagonals

Theory: