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Year 7 Interactive Maths - Second Edition


Area of a Rectangle

1 square centimetre

The area of a square that has a side-length of 1 cm is 1 square centimetre (or 1 cm2).  To find the area of a rectangle by the method of counting squares, we divide the rectangle into small squares of one centimetre side-length .

Consider a rectangle of length 5 cm and width 3 cm.

3 rows of 5 squares

Using the method of counting squares, we find that the area of the rectangle is 15 cm2.

Clearly, the rectangle contains 3 rows of 5 squares.  Therefore:

Area is 15 square centimetres


This suggests that:

The area of a rectangle is equal to its length multiplied by its width.  That is:

Area is equal to length times width

Using the pronumerals A for area, l for length and w for width, we can write it simply as:

A = lw

This is the formula for the area of a rectangle.


Example 2

Find the area of a rectangular field 20 m long and 10 m wide.

Solution:

Rectangle of length 20 m and width 10 m

The area of the field is 200 square metres


Note:

To find the area of a region enclosed within a plane figure, draw a diagram and write an appropriate formula.  Then substitute the given values and use a calculator, if necessary, to obtain the required area.


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