Calculate Perimeter: Equilateral Triangle with 7-Unit Sides

Perimeter Formula with Equal-sided Triangles

All of the sides of the triangle are equal. Calculate the perimeter of the triangle.

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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 triangle
00:03 The sides are equal according to the given data
00:11 The perimeter of the triangle equals the sum of its sides
00:16 Substitute in the side values and proceed to solve for the perimeter
00:23 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

All of the sides of the triangle are equal. Calculate the perimeter of the triangle.

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2

Step-by-step solution

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

  • Step 1: Recognize the triangle is equilateral with all sides having the same length.
  • Step 2: Apply the perimeter formula for an equilateral triangle.
  • Step 3: Calculate the perimeter using the provided side length.

Now, let's work through each step:
Step 1: We are given an equilateral triangle with one side length 77. All sides in an equilateral triangle are the same, so each side is 77.

Step 2: The formula for the perimeter PP of an equilateral triangle is given by:
P=3s P = 3s where ss is the side length of the triangle.

Step 3: Plugging our known side length s=7s = 7 into the formula, we have:
P=3×7=21 P = 3 \times 7 = 21

Therefore, the solution to the problem is 21.

3

Final Answer

21

Key Points to Remember

Essential concepts to master this topic
  • Definition: Equilateral triangles have three sides of identical length
  • Formula: Perimeter = 3 × side length, so P = 3 × 7 = 21
  • Check: Count all three sides: 7 + 7 + 7 = 21 units ✓

Common Mistakes

Avoid these frequent errors
  • Adding only two sides instead of all three
    Don't calculate 7 + 7 = 14 and stop there! This misses one entire side of the triangle. Always remember that perimeter means the total distance around ALL sides, so you must add all three equal sides: 7 + 7 + 7 = 21.

Practice Quiz

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Is the triangle in the drawing a right triangle?

FAQ

Everything you need to know about this question

What's the difference between an equilateral triangle and other triangles?

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An equilateral triangle has all three sides exactly the same length! Other triangles might have different side lengths, but equilateral triangles are special because all sides are equal.

Why is the formula P = 3s instead of just adding the sides?

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Both methods work! P = 3s is just a shortcut since all three sides are the same. Instead of writing 7 + 7 + 7, we can write 3 × 7 - it's faster!

How do I know if a triangle is equilateral just by looking?

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Look for equal markings on all three sides or check if all side lengths are labeled the same. In this problem, we're told 'all sides are equal' and one side shows 7 units.

What units should I use for the perimeter?

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Use the same units as the given side length. Since the side is 7 units, the perimeter is 21 units. If it were 7 cm, the perimeter would be 21 cm.

Can I use this formula for any triangle?

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Only for equilateral triangles! For other triangles, you need to add up each individual side length since they're all different. The formula P = 3s only works when all sides are equal.

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