What is the formula for calculating the perimeter of a rectangle?

Definition of rectangle

Kite Book, Math 3, Volume 1 defines a rectangle as a shape with 4 right angles, 2 equal long sides and 2 equal short sides.

Properties of rectangles

A rectangle has all the properties of an isosceles trapezoid and a parallelogram such as:

- Pairs of opposite sides are always parallel and equal.

- The angles are equal and 90 degrees.

- Rectangles have symmetry through the diagonals and through the midpoints of the sides.

Signs to recognize a rectangle

- A quadrilateral with three right angles is a rectangle.

- An isosceles trapezoid with one right angle is a rectangle.

- A parallelogram with one right angle is a rectangle.

- A face with two equal diagonals is a rectangle.

Formula for calculating the perimeter of a rectangle

According to the Math 3 textbook, to calculate the perimeter of a rectangle, we take the length plus the width (same unit of measurement) and then multiply by 2.

P = (a+b) x 2

In there

P is the perimeter of the rectangle.

a is the length of the rectangle.

b is the width of the rectangle.

For example: Calculate the perimeter of a rectangle with length 6cm and width 4cm.

Answer: The perimeter of the rectangle is P = (6+4) x 2 = 20 (cm).

Compare rectangles and squares

Criteria	Rectangle	Square
Edge	4 sides, 2 pairs of opposite sides are equal	4 sides, all 4 sides are equal
Corner	4 right angles	4 right angles
Diagonal	Two diagonals are equal, intersect at the midpoint but are not perpendicular	Two diagonals are equal, intersect at midpoint and are perpendicular to each other.
Formula for calculating perimeter	P = (a+b) x 2	P = 4a
Formula for calculating area	S = axb	S = a2

Formula for calculating the area of a rectangle To calculate the area of a rectangle, in addition to multiplying the length by the width, it can also be calculated when knowing one side and adding the diagonal or perimeter.

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