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

Calculate the perimeter of the parallelogram ABCD, given that CD is parallel to AB.

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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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