Areas of Polygons for 7th Grade

🏆Practice area of a rectangle

Areas of Polygons

Polygon Definition

A polygon defines a geometric shape that is made up of sides. In other words, under the umbrella of polygons fall the following square, rectangle, parallelogram, trapezoid, and many more.

For example, a triangle has 3 sides, every quadrilateral has 4 sides, and so on.

We have already learned to calculate the areas of standard polygons. There are also non-standard polygons, for which there is no specific formula. However, their area of complex shapes can be calculated using two methods:

  • We can divide the area of the required polygon into several areas of polygons that we are familiar with, calculate the areas separately, and then add them together to obtain the final area.
  • We can try to "complete" the area of the required polygon into another polygon whose area we know how to calculate, and the proceed to subtract the area we added. This way, we can obtain the area of the original polygon.

Example

Let's demonstrate this using a simple exercise:

Diagram of a composite shape divided into two rectangles, with dimensions labeled. The left rectangle has dimensions 7 by 4 with an area (A) of 28, and the right rectangle has dimensions 3 by 6 with an area (A) of 18. The diagram illustrates how to calculate areas of composite polygons by dividing them into simpler shapes. Featured in a tutorial on calculating areas of polygons.

Here is a drawing of a polygon.

We need to calculate its area. From the start, we can see that this is not a standard polygon, so we will use the first method to calculate its area. We will divide the polygon as shown in the drawing, and we should obtain two rectangles.

According to the data shown in the drawing, in the rectangle on the right side we obtain the side lengths of 3 and 6, therefore the area of the rectangle will be 18 (multiplication of the two values). In the rectangle on the left side we obtain the side lengths of 4 and 7, therefore the area of the rectangle will be 28 (multiplication of the two values). Thus, the total area of the polygon will be the sum of the two areas we calculated separately, meaning, 18+28=46.

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Test yourself on area of a rectangle!

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What is the area of the given triangle?

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In 7th grade we focus on learning about several polygons (click on the links for in-depth reading):

How to calculate areas of polygons

The formula for calculating the area of a polygon varies according to the polygon in question. (Click on the titles to read the full articles including examples and practice)

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Test your knowledge

Calculating Rectangle Area

The formula for calculating the area of a rectangle is: width X length.

S=whS=w\cdot h

A2 - Rectangle area formula

Calculating the area of any triangle

The formula for calculating the area of any triangle: base X height divided by 2

S=Baseh2S={{Base \cdot h}\over 2}

A3 - Triangle Area Formula

Do you know what the answer is?

Calculating the area of a right triangle

In the case of a right triangle's area, it's the same formula, but the height is actually one of the sides

A - area of a new right triangle

Calculating the Area of a Parallelogram

The area of a parallelogram is calculated by multiplying one of its sides by the height.

S=Baseh2S={{Base \cdot h}\over 2}

For example in the drawing, you can calculate the area of the parallelogram by multiplying DC by h1 and then dividing by 2, or by multiplying BC by h2 and then dividing by 2

1 - Area of a Parallelogram

Check your understanding

Calculating the Area of a Trapezoid

The formula for calculating the area of a trapezoid is the sum of the two bases X the height divided by 2

S=(Base1+Base2)h2S={{(Base{_1} + Base{_2}) \cdot h}\over 2}

A1 - How do you calculate the area of a new trapezoid

Do you think you will be able to solve it?

Examples with solutions for Areas of Polygons for 7th Grade

Exercise #1

What is the area of the given triangle?

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Video Solution

Step-by-Step Solution

This question is a bit confusing. We need start by identifying which parts of the data are relevant to us.

Remember the formula for the area of a triangle:

A1- How to find the area of a triangleThe height is a straight line that comes out of an angle and forms a right angle with the opposite side.

In the drawing we have a height of 6.

It goes down to the opposite side whose length is 5.

And therefore, these are the data points that we will use.

We replace in the formula:

6×52=302=15 \frac{6\times5}{2}=\frac{30}{2}=15

Answer

15

Exercise #2

What is the area of the triangle in the drawing?

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Video Solution

Step-by-Step Solution

First, we will identify the data points we need to be able to find the area of the triangle.

the formula for the area of the triangle: height*opposite side / 2

Since it is a right triangle, we know that the straight sides are actually also the heights between each other, that is, the side that measures 5 and the side that measures 7.

We multiply the legs and divide by 2

5×72=352=17.5 \frac{5\times7}{2}=\frac{35}{2}=17.5

Answer

17.5

Exercise #3

Calculate the area of the parallelogram based on the data in the figure:

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Video Solution

Step-by-Step Solution

In this particular problem, despite being given certain measurements, the diagram lacks sufficient clarity to identify which corresponds definitively as the base and which as the perpendicular height of the parallelogram. This insufficiency means that without further context or labeling to avoid assumptions that may lead to error, it is not feasible to calculate the area confidently using the standard formula.

Thus, the answer to the problem is that it is not possible to calculate the area with the provided data.

Answer

It is not possible to calculate.

Exercise #4

A parallelogram has a length equal to 6 cm and a height equal to 4.5 cm.

Calculate the area of the parallelogram.

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Video Solution

Step-by-Step Solution

To solve this problem, let's apply the formula for the area of a parallelogram:

The formula for the area of a parallelogram is Area=base×height \text{Area} = \text{base} \times \text{height} .

Here, the base of the parallelogram is 6 cm, and the height is 4.5 cm.

Substituting these values into the formula gives:

Area=6×4.5 \text{Area} = 6 \times 4.5

Performing the multiplication:

Area=27 \text{Area} = 27 square centimeters.

Therefore, the area of the parallelogram is 27cm2 27 \, \text{cm}^2 .

Referring to the given multiple-choice answers, the correct choice is:

Choice 3: 27 27 .

Answer

27

Exercise #5

Calculate the area of the parallelogram using the data in the figure:

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Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the given information
  • Step 2: Apply the appropriate formula
  • Step 3: Perform the necessary calculations

Now, let's work through each step:
Step 1: The problem provides us with a base (bb) of 7 units and a height (hh) of 5 units, perpendicular to this base.
Step 2: We'll apply the formula for the area of a parallelogram, which is Area=b×h \text{Area} = b \times h .
Step 3: Substituting the given values, Area=7×5=35 \text{Area} = 7 \times 5 = 35 .

Therefore, the area of the parallelogram is 35 35 square units.

Answer

35

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