math
4th Grade - Geometry

4th Grade lesson

4 - Geometry


Area of a figure

The area of a figure coranswers to the number of squares whose sides measure 1, that you can place inside the figure.
For example in the following rectangle you can place inside 8 squares of length 1 cm, we say that the area of the rectangle is 8 cm square (or 8 cm²).
area
In the following figure, you can place at least 8 squares of length 1 cm so the area of the figure is bigger than 8 cm².
area
The area of a square is always equal to the length of its side multiplied by itself. For example if a side of a square measures 10 cm, then the area of the square is equal to 10 times 10 cm square, or 100 cm²
The area of a rectangle is always equal to the length of its biggest side multiplied by the length of its smallest one. For example if a rectangle has sides of 4,7,4 and 7 cm, then its area is equal to 4 times 7 cm square, or 28 cm².

Volume of a solid

The volume of a solid is the number of little cubes whose sides measure 1, that you can place inside. In the following example, you can place 28 little cubes of side 1 cm inside of the pave so you can say that the volume is 28 cm cube (cm³).
volume
In general :
The volume of a pave, is equal to the length of a side multiplied by the length of another side, all this multiplied by the heigth of the pave.
The volume of a cube is equal to the length of a side multiplied by itself twice. For instance if a side of a cube measure 3 cm, then its volume is equal to 3 times 3 times 3 cm cube, or 27 cm³

Symetry of a figure

You can say that a figure is symetrical according to an axis of symetry if, folding the figure along this axis, the points of the figure of one side are exactly at the same place than the points on the other side of the axis.
symetry
Non symetrical figure
symetry
Symetrical figure (green axis)
Non symetrical figure (you cannot find an axis of symetry)
Symetrical figure (green axis)



See also : geometry on fmaths.com



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Geometry Grade 4

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