Perimeter is the distance around the outside of an object, but Area is the amount of space inside a two dimensional flat object.
In this post we look at the area of geometric shapes. However we do not look at Compound Areas or Circles, as these will be covered in other posts.
Areas are Important for Surveyors, Town Planners, and Councils.
Aeronautical Engineers work out the areas of aircraft wings when investigating aerodynamic properties and designs.
Area is also very important for Builders, when quoting for costs of materials.
People who work with lighting and media projectors need to understand the mathematics involved with the dispersion and intensity of light.
Now that we know how important Area is to our everyday lives, let’s start looking at the Mathematics of calculating areas.
Here is a great music video to watch all about Perimeter and Area.
Different shapes have different area formulas.
Area of a Rectangle
A very simple shape is the “Rectangle”.
We can prove this formula by drawing a whole bunch of rectangles, and counting how many squares are inside them.
However, not all shapes are as simple as a Rectangle. If we push a Rectangle sideways, we from a Parallelogram.
Area of a Parallelogram
The Area of a Parallelogram is Area = base x height
Here is a video all about the Area of a Parallelogram.
How do you like this for a real life Parallelogram!
Area of a Triangle
We could work out the area of a triangle by drawing it to scale on grid paper and counting squares.
This formula can be worked out very easily, because a Triangle is half of a Parallelogram.
Area of any Parallelogram is Area = base x height.
So the area of any Triangle is : Area = 1/2 x base x height.
Here is a video that explains how this works.
Here is an example of how we calculate the area of a triangle.
Note that the above example used “FISC” working out steps.
Substitution of values into Formula
Calculate the final answer and make sure it has square units on it. Eg. sq cm, sq inches, sq km, and so on.
It is vitally important to always show these steps when calculating the area of any shape.
Area of a Trapezium (or Trapezoid).
This shape is a bit like a Parallelogram, except that it only has two parallel sides.
Australians call it a “Trapezium”, and Americans call it a “Trapezoid”.
Here is a quick little video to help remember how to calculate the area of a Trapezium.
Area of a Rhombus
A Rhombus is a Parallelogram that has all four sides equal. We can work out its area using Base x Height, but we can also work out the same area by multiplying the two internal diagonals together, and dividing by 2.
Answers to Rhombus Questions:
Q1. 418 sq cm, 41600 sq mm, 0.0006 sq m.
Q2. 91 sq cm
Q3. (1000×2) / 10 = 200mm.
Q4. (120×2) / 30 = 8m.
Area of a Kite
A Kite is a similar shape to a Rhombus, and its area is obtained by multiplying together its diagonals.
Summary of Area Formulas
Here is a set of formulas that are used in mathematics for finding areas.
Here is an Online learning Activity to do that is all about Perimeter and Area
Here is an activity on Areas of Rectangles, Triangles, and Parallelograms.
(This one takes a little while to load up).
Click the question mark to enter your answer, then click the ok to check your answer.
Online Area and Perimeter Games
Play this fun game where we use basic Area and Perimeter skills to design zoo enclosures for animal exhibits:
Play this interesting game to find the relationship between Perimeter and Area.
Have some fun learning about irregular shaped areas with this Tangrams game.
A Challenging Area and Perimeter Game
It is necessary to get right on the corners of the initial symbols, get the hand symbol, and then drag the items around the grid to make them fit according to the Perimeter and Area rules given.
Note that final areas of items are not allowed to overlap. However, it might be necessary to do some overlapping while making the shapes.
Test Yourself Online
Click the link below for an Online Lesson on Area of Triangles, and scroll down the page to do a five question online test.
Click the link below for an Online Lesson on Area of Parallelograms, and a five question online test.
Click the link below for an Online Lesson on Area of Trapeziums, and a five question online test.
Here is an Online Quiz on Areas of Rectangles and Parallelograms, that includes finding unknown sides, if Area is known.
Try these mixed practice questions on Perimeter and Area.
Here is one final set of mixed problems.
Hope this has covered all areas !
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