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What is perimeter? How to find the perimeter? Perimeter of a square and rectangle. Determination methods and examples of solutions What does the perimeter of a rectangle mean? |
Lesson and presentation on the topic: "Perimeter and area of a rectangle"Additional materials Teaching aids and simulators in the Integral online store for grade 3
What are rectangle and squareRectangle is a quadrilateral with all right angles. This means that opposite sides are equal to each other. Square is a rectangle with equal sides and equal angles. It is called a regular quadrilateral. Quadrangles, including rectangles and squares, are designated by 4 letters - vertices. Latin letters are used to designate vertices: A, B, C, D... Example. What is the perimeter of a rectangle? Formula for calculating perimeterPerimeter of a rectangle is the sum of the lengths of all sides of the rectangle or the sum of the length and width multiplied by 2.The perimeter is indicated by a Latin letter P. Since the perimeter is the length of all sides of the rectangle, the perimeter is written in units of length: mm, cm, m, dm, km. For example, the perimeter of rectangle ABCD is denoted as P ABCD, where A, B, C, D are the vertices of the rectangle. Let's write down the formula for the perimeter of a quadrilateral ABCD: P ABCD = AB + BC + CD + AD = 2 * AB + 2 * BC = 2 * (AB + BC) Example. Given a rectangle ABCD with sides: AB=CD=5 cm and AD=BC=3 cm. Let's define P ABCD. Solution: P ABCD = 2 * (AB + BC) P ABCD = 2 * (5 cm + 3 cm) = 2 * 8 cm = 16 cm Answer: P ABCD = 16 cm. Formula for calculating the perimeter of a squareWe have a formula for determining the perimeter of a rectangle.P ABCD = 2 * (AB + BC) Let's use it to determine the perimeter of a square. Considering that all sides of the square are equal, we get: P ABCD = 4 * AB Example. Given a square ABCD with a side equal to 6 cm. Let us determine the perimeter of the square. Solution. 2. Let us recall the formula for calculating the perimeter of a square: P ABCD = 4 * AB 3. Let’s substitute our data into the formula: P ABCD = 4 * 6 cm = 24 cm Answer: P ABCD = 24 cm. Problems to find the perimeter of a rectangle1. Measure the width and length of the rectangles. Determine their perimeter. 3. Draw a square SEOM with a side of 5 cm. Determine the perimeter of the square. Where is the calculation of the perimeter of a rectangle used?1. A plot of land has been given; it needs to be surrounded by a fence. How long will the fence be?
2. Parents decided to renovate the children's room. You need to know the perimeter of the room and its area in order to correctly calculate the amount of wallpaper. What is the area of a rectangle?Square is a numerical characteristic of a figure. Area is measured in square units of length: cm 2, m 2, dm 2, etc. (centimeter squared, meter squared, decimeter squared, etc.)In calculations it is denoted by a Latin letter S. To determine the area of a rectangle, multiply the length of the rectangle by its width. S AKMO = AK * KM Example. What is the area of rectangle AKMO if its sides are 7 cm and 2 cm? S AKMO = AK * KM = 7 cm * 2 cm = 14 cm 2. Answer: 14 cm 2. Formula for calculating the area of a squareThe area of a square can be determined by multiplying the side by itself.Example. S ABCO = AB * BC = AB * AB Example. Determine the area of a square AKMO with a side of 8 cm. S AKMO = AK * KM = 8 cm * 8 cm = 64 cm 2 Answer: 64 cm 2. Problems to find the area of a rectangle and square1. Given a rectangle with sides 20 mm and 60 mm. Calculate its area. Write your answer in square centimeters.2. A dacha plot measuring 20 m by 30 m was purchased. Determine the area of the dacha plot and write the answer in square centimeters. In this lesson we will introduce a new concept - the perimeter of a rectangle. We will formulate a definition of this concept and derive a formula for its calculation. We will also repeat the combinational law of addition and the distributive law of multiplication. In this lesson we will learn about the perimeter of a rectangle and its calculation. Consider the following geometric figure (Fig. 1): Rice. 1. Rectangle This figure is a rectangle. Let's remember what distinctive features of a rectangle we know. A rectangle is a quadrilateral with four right angles and equal sides. What in our life can have a rectangular shape? For example, a book, a table top or a plot of land. Consider the following problem: Task 1 (Fig. 2) The builders needed to put up a fence around the plot of land. The width of this section is 5 meters, the length is 10 meters. What length of fence will the builders get? Rice. 2. Illustration for problem 1 The fence is placed along the boundaries of the site, therefore, to find out the length of the fence, you need to know the length of each side. This rectangle has equal sides: 5 meters, 10 meters, 5 meters, 10 meters. Let's create an expression for calculating the length of the fence: 5+10+5+10. Let's use the commutative law of addition: 5+10+5+10=5+5+10+10. This expression contains sums of identical terms (5+5 and 10+10). Let's replace the sums of identical terms with products: 5+5+10+10=5·2+10·2. Now let's use the distributive law of multiplication relative to addition: 5·2+10·2=(5+10)·2. Let's find the value of the expression (5+10)·2. First we perform the action in brackets: 5+10=15. And then we repeat the number 15 twice: 15·2=30. Answer: 30 meters. Perimeter of a rectangle- the sum of the lengths of all its sides. Formula for calculating the perimeter of a rectangle: , here a is the length of the rectangle, and b is the width of the rectangle. The sum of length and width is called semi-perimeter. To obtain the perimeter from the semi-perimeter, you need to increase it by 2 times, that is, multiply by 2. Let's use the formula for the perimeter of a rectangle and find the perimeter of a rectangle with sides 7 cm and 3 cm: (7 + 3) 2 = 20 (cm). The perimeter of any figure is measured in linear units. In this lesson we learned about the perimeter of a rectangle and the formula for calculating it. The product of a number and the sum of numbers is equal to the sum of the products of the given number and each of the terms. If the perimeter is the sum of the lengths of all sides of the figure, then the semi-perimeter is the sum of one length and one width. We find the semi-perimeter when we work according to the formula for finding the perimeter of a rectangle (when we perform the first action in parentheses - (a+b)). Bibliography
Homework
A rectangle has many distinctive features, based on which rules for calculating its various numerical characteristics have been developed. So, a rectangle: Flat geometric figure; The perimeter is the total length of all sides of the figure. Calculating the perimeter of a rectangle is a fairly simple task. All you need to know is the width and length of the rectangle. Since a rectangle has two equal lengths and two equal widths, only one side is measured. The perimeter of a rectangle is equal to twice the sum of its two sides, length and width. P = (a + b) 2, where a is the length of the rectangle, b is the width of the rectangle. The perimeter of a rectangle can also be found using the sum of all sides. P= a+a+b+b, where a is the length of the rectangle, b is the width of the rectangle. The perimeter of a square is the length of the side of the square multiplied by 4. P = a 4, where a is the length of the side of the square. Addition: Finding the area and perimeter of rectanglesThe curriculum for grade 3 includes the study of polygons and their features. In order to understand how to find the perimeter of a rectangle and area, let's figure out what is meant by these concepts. Basic ConceptsFinding perimeter and area requires knowledge of some terms. These include:
When becoming familiar with polygons, their vertices may be called ABCD. In mathematics, it is customary to name points in drawings with letters of the Latin alphabet. The name of the polygon lists all the vertices without gaps, for example, triangle ABC. Perimeter calculationThe perimeter of a polygon is the sum of the lengths of all its sides. This value is denoted by the Latin letter P. The level of knowledge for the proposed examples is 3rd grade. Problem #1: “Draw a rectangle 3 cm wide and 4 cm long with vertices ABCD. Find the perimeter of rectangle ABCD." The formula will look like this: P=AB+BC+CD+AD or P=AB×2+BC×2. Answer: P=3+4+3+4=14 (cm) or P=3×2 + 4×2=14 (cm). Problem No. 2: “How to find the perimeter of a right triangle ABC if the sides are 5, 4 and 3 cm?” Answer: P=5+4+3=12 (cm). Problem No. 3: “Find the perimeter of a rectangle, one side of which is 7 cm and the other is 2 cm longer.” Answer: P=7+9+7+9=32 (cm). Problem No. 4: “The swimming competition took place in a pool whose perimeter is 120 m. How many meters did the competitor swim if the pool is 10 m wide?” In this problem the question is how to find the length of the pool. To solve, find the lengths of the sides of the rectangle. The width is known. The sum of the lengths of the two unknown sides should be 100 m. 120-10×2=100. To find out the distance covered by the swimmer, you need to divide the result by 2. 100:2=50. Answer: 50 (m). Area calculationA more complex quantity is the area of the figure. Measurements are used to measure it. The standard among measurements is squares. The area of a square with a side of 1 cm is 1 cm². A square decimeter is denoted as dm², and a square meter is denoted as m². The areas of application of units of measurement can be:
If you draw a rectangle 3 cm long and 1 cm wide and divide it into squares with a side of 1 cm, then it will fit 3 squares, which means its area will be 3 cm². If the rectangle is divided into squares, we can also find the perimeter of the rectangle without difficulty. In this case it is 8 cm. Another way to count the number of squares that fit into a shape is to use a palette. Let's draw a square on tracing paper with an area of 1 dm², which is 100 cm². Place the tracing paper on the figure and count the number of square centimeters in one row. After this, we find out the number of rows, and then multiply the values. This means that the area of a rectangle is the product of its length and width. Ways to compare areas:
Example No. 1: “A seamstress sewed a baby blanket from square multi-colored scraps. One piece 1 dm long, 5 pieces in a row. How many decimeters of tape will a seamstress need to process the edges of a blanket if the area is 50 dm²?” To solve the problem, you need to answer the question of how to find the length of a rectangle. Next, find the perimeter of a rectangle made up of squares. From the problem it is clear that the width of the blanket is 5 dm; we calculate the length by dividing 50 by 5 and get 10 dm. Now find the perimeter of a rectangle with sides 5 and 10. P=5+5+10+10=30. Answer: 30 (m). Example No. 2: “During the excavations, an area was discovered where ancient treasures may be located. How much territory will scientists have to explore if the perimeter is 18 m and the width of the rectangle is 3 m? Let's determine the length of the section by performing 2 steps. 18-3×2=12. 12:2=6. The required territory will also be equal to 18 m² (6×3=18). Answer: 18 (m²). Thus, knowing the formulas, calculating the area and perimeter will not be difficult, and the above examples will help you practice solving mathematical problems. Class: 2 Target: introduce the method of finding the perimeter of a rectangle. Tasks: develop the ability to solve problems related to finding the perimeter of figures, develop the ability to draw geometric shapes, consolidate the ability to calculate using the commutative property of addition, develop the skill of mental calculation, logical thinking, cultivate cognitive activity and the ability to work in a team. Equipment: ICT (multimedia projector, presentation for the lesson), pictures with geometric shapes for physical education, a model of a magic square, students have models of geometric shapes, marker boards, rulers, textbooks, notebooks. DURING THE CLASSES 1. Organizational moment Checking readiness for the lesson. Greetings.
2. Oral counting a) Use of magical figures. ( Annex 1 ) – Fill in the cells of the magic square, name its features (the sum of the numbers along the horizontal, vertical and diagonal lines is equal) and determine the magic number. (39) Along the chain, children fill in the square on the board and in their notebooks. b) Acquaintance with the properties of magic triangles. ( Appendix 2 ) – The sums of the numbers in the angles forming a triangle are equal. Let's find the magic numbers for the triangle. Find the missing number. Mark it on the marker board. 3. Preparing to study new material – In front of you are geometric shapes. Name them in one word. (Quadrangles). 4. Study a new topic – Read the topic of our lesson: “Perimeter of a rectangle.” ( Appendix 4
) Those who wish find R at the board. Students write down the solution in their notebooks. – How can I write this differently?
– We have obtained a formula for finding the perimeter of a rectangle. ( Appendix 5 ) 5. Consolidation Page 44 No. 2. Children read and write down a condition, a question, draw a figure, find P in different ways, and write down the answer. 6. Physical exercise. Signal cards
7. Practical work – On your desks there are geometric shapes in envelopes. What should we call them? Mutual check of notebooks. – Read: How did you find the perimeter? What can be said about the perimeters of these figures? (They are equal).
8. Graphic dictation There are 6 cells on the left. We've made a point. Let's start moving. 2 – right, 4 – down right, 10 – left, 4 – up right. What figure? Turn it into a rectangle. Finish it. Find R in different ways.
9. Finger gymnastics
(Words are accompanied by movements) 10. Drawing up and solving a problem according to the condition(Appendix 8 ) Rectangle length – 12 dm 11. Independent work 12. Lesson summary - What did you learn? How did you find the P of a rectangle? 13.Assessment Students' answers are assessed at the board and selectively during independent work. 14.Homework P. 44 No. 5 (with explanations). Perimeter is the sum of the lengths of all sides of the polygon.
Distinctive features of a rectangle
How to calculate the perimeter of a rectangleThere are 2 ways to find it:
"a"- the length of a rectangle, the longer pair of its sides. "b"- the width of the rectangle, the shorter pair of its sides. An example of a problem to calculate the perimeter of a rectangle:Calculate the perimeter of the rectangle, its width is 3 cm, and its length is 6. Remember the formulas for calculating the perimeter of a rectangle!Semiperimeter is the sum of one length and one width .
How to find the area of a rectangleRectangle area formula S= a*b If the length of one side and the length of the diagonal are known in the condition, then the area can be found using the Pythagorean theorem in such problems; it allows you to find the length of a side of a right triangle if the lengths of the other two sides are known.
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