新北师大版三年级下册数学第五单元《面积》知识点总结(全)
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新北师大版三年级下册数学第五单元《面积》知识点总结(全)
Unit 5 of Grade 3: Summary of Knowledge Points on "Area"
I。Concept of Area
The size of an object's surface or a closed shape is its area.
The length around a closed shape is called the perimeter.
II。Units of Area
1.To compare the sizes of two shapes。we need to measure
them using the same unit of area.
mon units of area include square centimeters (cm2)。square decimeters (dm2)。and square meters (m2).
For example。a square with a side length of 1 cm has an area
of 1 square centimeter。a square with a side length of 1 dm has an
area of 1 square decimeter。which is equal to 100 square
centimeters。a square with a side length of 1 m has an area of 1
square meter。which is equal to 100 square decimeters. Examples of objects that are close to 1 square centimeter。1
square decimeter。and 1 square meter in real life are a fingernail。the palm of a hand or an electrical outlet。and a ___ board on the
side of a classroom。respectively.
III。n of Units of Area
1.n rates een units of area:
1 dm2 = 100 cm2
___ decimeters to square centimeters。add two zeros to the
end of the number。to convert ___ decimeters。remove two zeros
from the end.
1 m2 = 100 dm2
___ square meters to square decimeters。add two zeros to the
end of the number。to convert square decimeters to square meters。remove two zeros from the end.
1 m2 = 10,000 cm2
___ square meters to square centimeters。add four zeros to
the end of the number。to convert square centimeters to square
meters。remove four zeros from the end.
mon units of length include centimeters (cm)。decimeters (dm)。and meters (m).
___:
1 cm = 10 mm
1 dm = 10 cm
1 m = 10 dm = 100 cm
1 km = 1000 m
IV。Difference een Units of Length and Units of Area
Units of length measure the length of a line segment。while
units of area measure the size of a surface。Therefore。the units
of length and area are not the same and cannot be compared。We
need to distinguish when to use units of length and when to use
units of area.
V。Area and Perimeter of Rectangles and Squares
1.Formulas for the area and perimeter of a rectangle:
Area of a rectangle = length × width
Perimeter of a rectangle = (length + width) × 2
To find the length: length = area ÷ width To find the width: width = area ÷ length
To find the length when the perimeter is known: length =
perimeter ÷ 2 - width
To find the width when the perimeter is known: width =
perimeter ÷ 2 - length
2.Formulas for the area and perimeter of a square:
Area of a square = side length × side length
Perimeter of a square = side length × 4
