Công thức tính diện tích hình chữ nhật và bài tập thực hành chi tiết

Calculating the area of ​​a rectangle is basic knowledge of geometry. But for children in elementary school, there will still be many surprises when learning. So, in the following article, let’s learn more about this knowledge with Nguyễn Tất Thành.

Review rectangular theory

Before learning how to calculate and calculate the area of ​​a rectangle, let’s review some basic knowledge about rectangles with Nguyễn Tất Thành (including: definition, properties, theorems, recognition signs) right away. hereafter.

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What is the definition of a rectangle?

A rectangle is simply understood as a quadrilateral with 4 right angles, or a special parallelogram.

Properties of rectangles

Rectangles have some properties to remember as follows:

• A rectangle has two opposite sides parallel and equal.
• A rectangle has 4 equal corners (right angles/90 degrees).
• A rectangle has 2 equal diagonals that intersect at the midpoint of each line (forming 4 equilateral triangles, with 2 pairs of opposite triangles being congruent).

Rectangular identification sign

Some signs that you can use to identify rectangles are as follows:

• A quadrilateral with 3 right angles is a rectangle (because the sum of the angles in a quadrilateral is 360 degrees -> the remaining angle is also 90 degrees).
• If an isosceles trapezoid has one right angle, it is a rectangle.
• If a parallelogram has one right angle, it is a rectangle.
• A quadrilateral placed on a plane with two equal diagonals is a rectangle.

Formula to calculate the area of ​​a rectangle

The area of ​​a rectangle is the portion measured by the size of the surface of the shape, which is the plane part that we can see. So, to calculate the area of ​​a shape we will multiply the length by the width. The formula is as follows: S = axb

In there:

• S is the area of ​​the rectangle

• a is the length of the rectangle

• b is the width of the rectangle

For example: Given rectangle ABCD, length 5cm, width 3cm. Calculate the area of ​​figure ABCD.

The area of ​​rectangle ABCD is:

5 x 3 = 15 cm2

Answer: 15 cm2

Besides understanding how to calculate the area of ​​a rectangle, in mathematics you also need to memorize the formula for calculating the perimeter of a rectangle (to apply to problems calculating area based on the perimeter of a rectangle). .

The perimeter of a rectangle has the following formula:

P = (a + b) x 2

In there:

• P: perimeter of rectangle
• a: length of the rectangle
• b: width of the rectangle

Why is it necessary to calculate the area of ​​a rectangle?

As for clearly understanding the formula for calculating the area of ​​a rectangle, it is not only applied in elementary school mathematics, but when students reach higher grades they will still be familiar with it but at a more difficult level.

Besides, this knowledge is also applied in many different fields from surveying, construction, design, measurement, etc. Therefore, mastering the basic knowledge base is very important not only for Children, students, and even adults are very necessary.

Common types of elementary school rectangular area calculations

In mathematics, there are many types of math related to calculating the area of ​​different rectangles. But at the elementary level, children will be familiar with the following two basic forms:

Form 1: Calculate the area of ​​a rectangle when knowing the length and width

This is considered the most basic form of exercise, when the problem usually gives information about length, width and requires calculating the area of ​​the corresponding shape. Therefore, to solve the exercise, everyone only needs to apply the formula S = axb correctly to find the answer.

For example: Calculate the area of ​​a rectangle with length 10cm and width 7cm:

Solution: Applying the formula we have: S= 10 x 7 = 70 (cm2).

Form 2: Calculate one side of a rectangle when knowing the area and length of one side

With this form of math, it will be the opposite of form 1 above, when the problem will give information about the area of ​​the rectangle, along with the length or width and ask to find the remaining side. Therefore, when solving, we will also apply the formula S = axb to deduce the exact edge information to be found. Specifically:

For example: Given a rectangular garden, know the area of ​​the garden is 10cm, know the width of the garden is 5cm. Calculate the length of that garden.

Solution: Applying the formula we have the length of the garden = 10 : 5 = 2cm

Math exercises related to rectangular area for children to practice

After you have firmly grasped the theory, here are some related exercises for your child to practice:

Lesson 1: A rectangular garden has a length of 28cm and a width of 1/4 of the length. Calculate the area of ​​the garden.

Lesson 2: A rectangle has a length of 20 cm and an area of ​​100 cm2. Calculate the width of the rectangle.

Lesson 3: Calculate the perimeter and area of ​​a rectangle whose width is 15cm and half the perimeter is 40cm?

Lesson 4: What is the area of ​​a rectangle with length 12cm and width 8cm?

Lesson 5: A rectangular garden is 36cm long and 1/4 the width of the length. What is the area of ​​the rectangle?

Lesson 6: A rectangle has a length of 24cm and an area of ​​386cm². What is the width of the rectangle?

Lesson 7: Find the remaining lengths of the rectangle knowing:

a, The width of the rectangle is 15cm and the area is 390cm²

b, The length of the rectangle is 34cm and the area is 748cm²

Lesson 8: Calculate

a. Calculate the area of ​​a rectangle with length 12cm and width 9cm

b. Calculate the area of ​​a rectangle with length 2m5cm and width 8cm

d. Calculate the area of ​​a rectangle with width 50mm and length 2dm4cm

Lesson 9: A rectangle has a perimeter of 60 cm. Know that the width is ⅔ of the length. Calculate the area of ​​that rectangle.

Lesson 10: A rectangle has a perimeter of 50cm. The length is 4 times the width. Calculate the area of ​​that rectangle.

Lesson 11: Given a rectangle, if you decrease the length by 3cm and increase the width by 2cm, you get a square with a perimeter of 32cm. Calculate the perimeter and area of ​​that rectangle.

Lesson 12: A rectangle has a length of 12cm. If the length is extended by 3cm, the area increases by 21cm². Calculate the perimeter and area of ​​the original rectangle.

Lesson 13: A rectangular cloth is 1m long and 36cm wide. What is the area of ​​the rectangular cloth in square centimeters?

Lesson 14: A rectangle has a perimeter of 44cm. If the width is increased by 7cm and the length is increased by 1cm, the result is 1 square. Calculate the area of ​​that rectangle.

Lesson 15: A rectangle has a length of 12cm. If the length is extended by 3cm, the area increases by 21cm². Calculate the perimeter and area of ​​the original rectangle.

The secret to helping children learn and remember the area of ​​a rectangle effectively

Knowledge of the area of ​​a rectangle at the elementary level is mainly at the basic level, but to ensure children understand and practice effectively. Here are some tips that parents can help their children:

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One of the things that many parents have difficulty with when teaching their children math is that their children are not focused, they learn quickly and get bored, easily “learning first and forgetting later”. Especially with math, children have difficulty absorbing it and are less interested in learning.

This difficulty comes from parents not having appropriate math teaching methods that create interest for children. So, try choosing Nguyễn Tất Thành Math to accompany your child and see.

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Make sure your child masters basic knowledge about rectangles

One of the important factors when solving the area of ​​a rectangle exercise correctly is to master the basic knowledge of this shape, from its characteristics, properties, formula for calculating the perimeter of a rectangle, area, and other factors. exercise format…

Because only when mastering this basic knowledge will children really understand how to solve exercises and practice correctly.

Therefore, parents need to test their children’s theory regularly by asking them questions such as “What is the formula to calculate the area of ​​a rectangle?”, “How to find the length of a rectangle?” when knowing the area?”…

Practice with your baby and practice more

After you have firmly grasped the theory, parents should create conditions for your child to practice more. From doing many exercises on calculating the area of ​​a rectangle from basic to advanced, learning more knowledge about rectangles on the internet, organizing small math competitions for children, creating related games. , study in groups with friends,…

Practicing more will help your child understand the nature of theory, know how to apply it when encountering exercises and solve problems, and increase the ability to remember and think effectively in math.

Learn the formula to calculate the area of ​​a rectangle through the poem

Besides the above tips, you can remember the formula for calculating the area and perimeter of a rectangle through the following poem:

How to calculate the area of ​​a rectangle?

It’s not difficult to multiply length by width

What is the perimeter of a rectangle needed?

The length plus the width is multiplied by two

– Collect –

Some notes when calculating the area of ​​a rectangle

In the process of solving the exercise on calculating the area of ​​a rectangle, to ensure accurate results, you need to pay attention to the following issues:

• Unit of measurement: When calculating the area of ​​a shape, make sure the lengths of the sides are in the same unit. If it is cm then all must be cm. If the units are different, it is necessary to convert to the same unit before performing the calculation.

• The unit of measurement for area is squared: when calculating the area of ​​a rectangle, many children often forget that their unit of measurement must be squared such as cm2, m2, dm2…

• Remember the exact formula: Because a rectangle is a special quadrilateral, the formula is easily confused with other quadrilaterals. So you need to understand clearly, if the formula is wrong, of course the result will also be wrong.

Conclude

Above is basic information about the area of ​​a rectangle. In general, when children clearly understand the formula, it will be easy to solve related exercises correctly. So, parents, please apply the above tips that Nguyễn Tất Thành shares to help your child learn and practice more effectively.

Nguồn: https://truongnguyentatthanh.edu.vn
Danh mục: Giáo dục