learn about perimeters of square rectangle triangle
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Contents 1. 2. 3. 4. 5. 6. Introduction Rectangles & Squares Activity Further Examples Area of Rectangles (counting squares) Key words for area of Rectangles
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Introduction The perimeter of a shape is the distance all the way round its edges. Perimeter is measured in units such as centimetres, feet or metres. The measurements needed to calculate a perimeter depend on the shape. For a rectangle you will need to know the length and width of the shape. (It is usual to call the longest side the length and the shortest the width or breadth.) Example 1 This diagram represents a pen for Jim's hens. How much netting does he need to go round the plot? All measurements are in metres. Here the length is 5 m and the width is 4 m. The perimeter of the plot is 18 So he needs 18 m of netting. 5m 5141
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Introduction Example 2 This diagram represents a pond that needs a low railing round the boundary. Sali is working out the perimeter. 1.2m 80cm All measurements used in the calculation must be in the same units. So she uses metres and works out 1.2 + 0.8 + 1.2 + 0.8 = 4.0 So the perimeter is 4 m
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Rectangles and Squares In a rectangle opposite sides are equal, so to work out the perimeter of a rectangle you just need to know the length and width. Example 1 6 cm 15 cm Here the length is 15 cm and the width 6 cm. Method 1 Length = 15 cm and width = 6 cm Perimeter = 15 + 6 + 15 + 6 = 42 cm Method 2 Because opposite sides are equal you can also work out the perimeter in this way: double the length, double the width, then add the results together. (15 x 2) + (6 x 2) = 30+12 = 42 Method 3 Add the length and width then double it. 15+6=21 21 x 2=42 The method you choose is up to you - each one will give the same answer.
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Rectangles and Squares Example 2 A square is a rectangle with four equal length sides. So you only need to know the measurement of one side. The perimeter of this shape can be worked out as 5+5+5+5= 20 m Or you can multiply the length by four. 5 x 4 = 20
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Match each shape to its perimeter with a straight line.. 6-5 6.5 m 1-3 10m 4 cm 7.5 m 7.5 m 12 cm 5 Cm 12 cm 9.5 m 6-5 m 9-5 m 6.5 m 6.7 1.3 m 6.7 10m 32 m 34 28 16 m 34 cm 16 cm
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Match each shape to its perimeter with a straight line.. 12 cm 12 cm 9. 6-5 m 9-5 m 4 crn 6-5 m 4 crn 7.5 m 7.5 m 1-3 m 10m 6-5 m 6.7 m 6.7 m 10m 32 34 28 16 m 34 cm 16 cm
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Further Examples Many practical examples of perimeters will not be as simple as the rectangle and squares shown in Factsheet 2, but remember that perimeter is the total length of the boundary of the shape. Example 1 18m 30 m 17m 22 m Kit's allotment is this shape. Work out the perimeter. You need to know all four lengths. 30 + 18 +22 + 17 = 87 m.
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Further Examples Example 2 25 cm Dennis wants to apply an ornamental strip to the edge of this planter. How much does he need? All the sides of this regular hexagon are equal, so a single measurement is all you need. You can work out 25 + 25 +25 +25 +25 + 25 = 150cm 1.5m) or use 25 x 150cm 1.5m)
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Further Examples Example 3 This flower bed has a low rail round it. What is its perimeter? The shape is symmetrical, so you do not need every length. Work your way round the twelve sides. Starting with the 4 m and moving round clockwise you get: 4+1+1+5+1+1+4+1+1+5+1+1= 26 m or 4+1+1 +5+1+1= 13 13 x 2=26 m
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Area of rectangles - counting squares Area is the space on a flat surface and measured in square unit There are many practical reasons for calculating the area of a flat surface. If you want to buy carpet for a room, the floor area has to be calculated so the correct amount of carpet can be ordered. The unit of measurement for areas is called square units. If you use metres to make your measurement, the area will be measured in square metres (m2). If centimetres are used, the area will be in square centimetres (cm2). The area of a rectangle can be calculated using two methods: ' counting squares ' multiplication
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Area of Rectangles & Squares Area by counting squares This square measures lcm long and lcm wide. It is 1 square centimetre (cm2). lcm 1 cm A rectangle drawn on the 1 cm2 paper below is 3 cm long and 2 cm wide. lcm lcm lcm lcm Count the number of 1 cm squares. There are 6 squares. So the area of the rectangle is 6 cm2.
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Key words for area of rectangles ' You'll come across some of these words when working out the area of rectangles. Have a look to see what they mean. rectangle area square units square centimetres square metres length width
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Key words for area of rectangles area The surface covered by any 2D or flat shape. ' rectangle A four sided shape with four right angles. length The longest side of the rectangle. width The shortest side of the rectangle. length A rectangle width
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Key words for area of rectangles ' square units Area is measured in square units, such as cm2 2 or m ' square centimetres A unit for measuring area. This shape is a unit square of 1 cm: The shape has an area of 1 cm2. 1 cm 1 cm
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Key words for area of rectangles ' square metres A unit for measuring area. If you measure a large area, such as a room, you should use metres. For example this field has an area of 60 rn2
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