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AREA AND PERIMETER
HYPERLINK "http://www.primarymath.net/7.html" Create grid.
Tip: Physically manipulate shapes by clicking and dragging.
SHAPE \* MERGEFORMAT
Area is the number of units that fit on a flat surface.
Each square(unit) on the grid is equal to 1cm2
What is the area of the rectangle? (Count the squares) 15 cm2
Can you think of a quicker way to find the area? LxB
Shade a rectangle with an area of 30cm2
Perimeter is the distance (number of units) around a shape
It may be measured in cm.
What is the perimeter of the rectangle above? Count the number of units around the rectangle (22 cm)
Think of a formula 2(l + b)
What is the area of the square? Count the square units: 9cm2
Quicker method: L x L
What is the perimeter of the square? Count the units: 12cm
Formula: L x 4
Examine these rectangles. Draw the grid lines and compare their areas.
Area = L x B Area = L x B
= 4cm x 3cm = 6cm x 2cm
= 12cm2 = 12cm2
Now compare the perimeters.
Perimeter = 2(L + B) Perimeter = 2(L + b)
= 2(4cm + 3cm) = 2(6cm + 2cm)
= 2 x 7cm = 2 x 8cm
= 14cm = 16cm
Therefore the relationship between area and perimeter is demonstrated. Area remains constant while perimeter is dynamic.
PS. Learners can physically manipulate the shapes by clicking on and dragging them to alter the area and perimeter. Perform practical activities e.g. illustrate garden with flower pots as the perimeter.
Now that you have discovered that area of a rectangle is l x b, look at the parallelogram below.
4cm
Area = l x b
3cm = 4cm x 3cm
= 12cm2
Calculate the area of the parallelogram. Find the shortest method. You may move the shape around.
4cm
3cm
Area of parallelogram = l x b
Examine the triangle below.
Calculate the area. Look at the rectangle and parallelogram.
The triangle is half the parallelogram and half the rectangle. Therefore the area of the triangle:
Area = (l x b) = (b x h)
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