Calculate Parallelogram Area: 22cm Perimeter with 2cm Height

Parallelogram Area with System of Equations

ABCD is a parallelogram whose perimeter is equal to 22 cm.

Side AB is smaller by 5 than side AD

The height of the parallelogram for the side AD is 2 cm

What is the area of the parallelogram?

AAABBBCCCDDD

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:13 Let's find the area of the parallelogram.
00:17 First, let's draw the height based on the information given.
00:21 Remember, the perimeter is the sum of all sides.
00:28 In a parallelogram, opposite sides are equal.
00:35 Look at side AD compared to side AB, as described in the data.
00:41 Let's plug in the values into the perimeter formula and solve for side AB.
01:01 Great! We found AB. Now, use it to determine the other sides.
01:13 Next, let's find the area. Multiply height 2 by side length 8.
01:21 And there you have it, the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

ABCD is a parallelogram whose perimeter is equal to 22 cm.

Side AB is smaller by 5 than side AD

The height of the parallelogram for the side AD is 2 cm

What is the area of the parallelogram?

AAABBBCCCDDD

2

Step-by-step solution

To solve this problem, we will follow these steps:

  • Step 1: Setup and solve the equations for side lengths ABAB and ADAD.
  • Step 2: Calculate the area using the base ADAD and the given height of 2 cm.

Let's begin:

Step 1: Calculate side lengths

Given that the perimeter is 22 cm, we have:

\begin{equation} 2(AB + AD) = 22 \end{equation}

The equation simplifies to:

\begin{equation} AB + AD = 11 \end{equation}

We are also given:

\begin{equation} AB = AD - 5 \end{equation}

Substitute this in the first equation:

\begin{equation} (AD - 5) + AD = 11 \end{equation} \begin{equation} 2AD - 5 = 11 \end{equation} \begin{equation} 2AD = 16 \end{equation} \begin{equation} AD = 8 \end{equation}

Now, substitute AD=8AD = 8 back into the expression for ABAB:

\begin{equation} AB = 8 - 5 = 3 \end{equation}

Step 2: Calculate the area

With AD=8AD = 8 cm as the base (since the problem specifies height to ADAD) and the given height of 2 cm, the area is calculated as:

\begin{equation} A = \text{base} \times \text{height} = 8 \times 2 = 16 \, \text{cm}^2 \end{equation}

Therefore, the area of the parallelogram is 16 cm².

3

Final Answer

16 cm²

Key Points to Remember

Essential concepts to master this topic
  • Perimeter Formula: For parallelograms, P=2(a+b) P = 2(a + b) where opposite sides are equal
  • System Technique: Set up equations: AB+AD=11 AB + AD = 11 and AB=AD5 AB = AD - 5
  • Area Check: Verify calculation: 8×2=16 8 \times 2 = 16 cm² using base × height ✓

Common Mistakes

Avoid these frequent errors
  • Using wrong base for area calculation
    Don't use AB (3 cm) as the base when height is given for AD! Using AB × 2 = 6 cm² gives the wrong answer. The height of 2 cm corresponds specifically to side AD. Always match the given height with its corresponding base.

Practice Quiz

Test your knowledge with interactive questions

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

Calculate the area of the parallelogram.

6664.54.54.5

FAQ

Everything you need to know about this question

Why can't I use side AB for the area calculation?

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The problem states "the height for side AD is 2 cm." This means the 2 cm height is perpendicular to side AD, not to side AB. Using AB would require a different height measurement.

How do I know which sides are opposite in a parallelogram?

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In parallelogram ABCD, opposite sides are AB and DC, and AD and BC. These pairs are always equal in length, which is why the perimeter formula is 2(AB+AD) 2(AB + AD) .

What if I get confused about which equation to substitute?

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Start with the simpler relationship first! Since AB=AD5 AB = AD - 5 is already solved for AB, substitute this into the perimeter equation AB+AD=11 AB + AD = 11 .

Can I verify my side lengths are correct?

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Yes! Check that AB = 3 cm and AD = 8 cm satisfy both conditions: AB + AD = 11 ✓ and AB is 5 less than AD ✓

Why is the area formula base × height and not length × width?

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For parallelograms, we use base × height where height is the perpendicular distance between parallel sides. This is different from a rectangle's length × width because parallelogram sides are slanted.

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