Calculate Rectangle Perimeter with Congruent Triangles: 6x8 Geometric Figure

Rectangle Perimeter with Congruent Triangle Properties

ΔAED≅ΔBCD

Calculate the perimeter of the rectangle AFDE.

AAABBBCCCEEEDDDFFF68

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine the perimeter of the rectangle AFDE
00:03 The triangles are congruent according to the given data
00:15 The sides are equal according to the theory of congruence
00:22 Substitute in the relevant values according to the given data
00:41 The opposite sides in a rectangle are equal
00:54 The perimeter of the rectangle equals the sum of its sides
01:05 Substitute in the relevant values and solve to determine the perimeter
01:26 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

ΔAED≅ΔBCD

Calculate the perimeter of the rectangle AFDE.

AAABBBCCCEEEDDDFFF68

2

Step-by-step solution

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

  • Step 1: Analyze the congruent triangles.

  • Step 2: Use congruence to identify side lengths.

  • Step 3: Calculate the perimeter of the rectangle.

Now, let's work through each step:
Step 1: The problem states that AEDBCD\triangle AED \cong \triangle BCD, which means corresponding sides and angles are equal.
Step 2: Identify corresponding sides from congruence:
- AE=CD=6AE = CD = 6 because corresponding sides of congruent triangles are equal.
- AD=BCAD = BC. Since AB=8AB = 8 and using the fact AED\triangle AED and BCD\triangle BCD are congruent, BDBD (the same as ADAD) must also equal 6 (from the congruence starting from point DD).
- Thus, AD=6AD = 6.

Step 3: Calculate the perimeter: AF=DE=6AF = DE = 6 from congruency and AD=FE=6AD = FE = 6. Since both pairs of opposite sides of the rectangle are equal, the rectangle perimeter is:
P=2(AF+AD)=2(6+8)=2×14=28 P = 2(AF + AD) = 2(6 + 8) = 2 \times 14 = 28

Therefore, the perimeter of the rectangle AFDEAFDE is 2828.

3

Final Answer

28

Key Points to Remember

Essential concepts to master this topic
  • Congruent Triangles: Corresponding sides are equal when triangles are congruent
  • Technique: Use AEDBCD\triangle AED \cong \triangle BCD to find AF = DE = 6
  • Check: Perimeter = 2(length + width) = 2(8 + 6) = 28 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing which sides correspond in congruent triangles
    Don't assume any two sides are equal without checking correspondence = wrong dimensions! This leads to incorrect perimeter calculations. Always identify corresponding parts using the congruence statement order: ΔAED≅ΔBCD means A↔B, E↔C, D↔D.

Practice Quiz

Test your knowledge with interactive questions

Look at the rectangle below.

Side DC has a length of 1.5 cm and side AD has a length of 9.5 cm.

What is the perimeter of the rectangle?

1.51.51.5AAABBBCCCDDD9.5

FAQ

Everything you need to know about this question

How do I know which sides are corresponding in the congruent triangles?

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Look at the order of letters in the congruence statement! In AEDBCD\triangle AED \cong \triangle BCD, the first letters (A and B) correspond, second letters (E and C) correspond, and third letters (D and D) correspond.

Why is AF equal to 8 and not 6?

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From the diagram, we can see that AF is part of side AB, and AB = 8. Since F divides AB, and from the congruent triangles we know the rectangle has width 6, AF must be 8 to form the rectangle's length.

What's the difference between finding triangle sides and rectangle sides?

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Triangle congruence helps us find corresponding equal sides, but for the rectangle perimeter, we need the rectangle's length and width. Use the congruent triangle information to determine these dimensions.

How can I double-check my rectangle dimensions?

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Verify that opposite sides are equal: AF should equal DE, and AD should equal FE. Also check that your dimensions make sense with the given measurements in the diagram.

What if I can't see the rectangle clearly in the figure?

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Focus on the points mentioned: rectangle AFDE means A, F, D, E are the four corners. Use the congruent triangle properties and given measurements to find the side lengths, then apply the rectangle perimeter formula.

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