Rectangle Perimeter: Calculate the Distance Around a 2cm × 7cm Shape

Q: Why do I need to add the same lengths twice?

Because a rectangle has four sides total! Even though opposite sides are equal, you still need to count each side as you walk around the perimeter. Think of it like walking around a fence - you pass each side once.

Q: Can I use a formula instead of adding all four sides?

Yes! You can use Perimeter = 2 × (length + width). For this rectangle: $ P = 2 × (7 + 2) = 2 × 9 = 18 $ cm. This is often faster than adding four separate numbers.

Q: What's the difference between perimeter and area?

Perimeter is the distance around the shape (like a fence), while area is the space inside the shape (like carpet). For perimeter, we add the sides. For area, we multiply length × width.

Q: How can I remember which sides are equal in a rectangle?

Think of a rectangle as having opposite sides equal. The top and bottom are the same length, and the left and right sides are the same length. It's like a stretched square!

Rectangle Perimeter with Given Side Lengths

Look at the rectangle below.

Side AB is 2 cm long and side BC has a length of 7 cm.

What is the perimeter of the rectangle?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:00 Calculate the perimeter of rectangle ABCD?

00:03 Opposite sides are equal in a rectangle

00:13 The perimeter of the rectangle equals the sum of its sides

00:23 Let's substitute appropriate values and solve for the perimeter

00:29 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Look at the rectangle below.

Side AB is 2 cm long and side BC has a length of 7 cm.

What is the perimeter of the rectangle?

Step-by-step solution

Given that in a rectangle every pair of opposite sides are equal to each other, we can state that:

$AB=CD=2$

$AD=BC=7$

Now we can add all the sides together and find the perimeter:

$2+7+2+7=4+14=18$

Final Answer

18 cm

Key Points to Remember

Essential concepts to master this topic

Property: Opposite sides of rectangles are equal in length
Formula: Add all four sides: 2 + 7 + 2 + 7 = 18 cm
Check: Perimeter equals 2 × (length + width) = 2 × (7 + 2) = 18 cm ✓

Common Mistakes

Avoid these frequent errors

Adding only two sides instead of all four
Don't just add 2 + 7 = 9 cm! This only gives you two sides, not the complete perimeter. A rectangle has four sides, so you must walk around the entire shape. Always add all four sides: 2 + 7 + 2 + 7 = 18 cm.

Practice Quiz

Test your knowledge with interactive questions

Look at the rectangle ABCD below.

Side AB is 6 cm long and side BC is 4 cm long.

What is the area of the rectangle?

FAQ

Everything you need to know about this question

Why do I need to add the same lengths twice?

Because a rectangle has four sides total! Even though opposite sides are equal, you still need to count each side as you walk around the perimeter. Think of it like walking around a fence - you pass each side once.

Can I use a formula instead of adding all four sides?

Yes! You can use Perimeter = 2 × (length + width). For this rectangle: $P = 2 × (7 + 2) = 2 × 9 = 18$ cm. This is often faster than adding four separate numbers.

What's the difference between perimeter and area?

Perimeter is the distance around the shape (like a fence), while area is the space inside the shape (like carpet). For perimeter, we add the sides. For area, we multiply length × width.

Do the units matter when calculating perimeter?

Yes! Always include the units in your final answer. Since both sides are measured in cm, the perimeter is also in cm. Never forget to write the units - it's part of the complete answer.

How can I remember which sides are equal in a rectangle?

Think of a rectangle as having opposite sides equal. The top and bottom are the same length, and the left and right sides are the same length. It's like a stretched square!

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