Calculate Circle Circumference with Radius = 11 Units: Step-by-Step Solution

Circumference Formula with Given Radius

r=11 r=11

Calculate the circumference.

111111

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate the circumference of the circle
00:03 We will use the formula for calculating circle circumference
00:06 We will substitute the radius according to the given data and solve for the circumference
00:14 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

r=11 r=11

Calculate the circumference.

111111

2

Step-by-step solution

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

  • Step 1: Identify the given information
  • Step 2: Apply the appropriate formula
  • Step 3: Perform the necessary calculations

Now, let's work through each step:
Step 1: The problem provides the radius of the circle as r=11 r = 11 .
Step 2: We'll use the formula for the circumference of a circle: C=2πr C = 2\pi r .
Step 3: Plugging in the value of the radius, r=11 r = 11 , into the formula, we get: C=2π×11=22π C = 2\pi \times 11 = 22\pi .
Using approximately π=3.14159\pi = 3.14159, we calculate: C=22×3.1415969.115 C = 22 \times 3.14159 \approx 69.115 .

Therefore, the circumference of the circle is approximately 69.115.

Upon comparing this with the given choices, the correct choice is:
Choice 4:

69.115

3

Final Answer

69.115

Key Points to Remember

Essential concepts to master this topic
  • Formula: Use C = 2πr where r is the radius
  • Technique: Substitute r = 11: C = 2π(11) = 22π
  • Check: Calculate 22 × 3.14159 = 69.115 matches answer choice ✓

Common Mistakes

Avoid these frequent errors
  • Using diameter formula instead of radius formula
    Don't use C = πd when given radius r = 11, this gives 11π ≈ 34.56! This is exactly half the correct answer because diameter is twice the radius. Always use C = 2πr when given the radius.

Practice Quiz

Test your knowledge with interactive questions

\( r=2 \)

Calculate the circumference.

222

FAQ

Everything you need to know about this question

What's the difference between radius and diameter?

+

The radius goes from the center to the edge of the circle, while the diameter goes all the way across through the center. Diameter = 2 × radius, so if r = 11, then d = 22.

Which π value should I use for calculations?

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For most problems, use π ≈ 3.14159 to get accurate decimal answers. Some problems might ask you to leave the answer in exact form as 22π instead.

Why do we multiply by 2 in the circumference formula?

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Think of it this way: the radius goes from center to edge, so 2r gives you the diameter. The circumference formula C = πd becomes C = π(2r) = 2πr!

How can I remember the circumference formula?

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Remember: C = 2πr sounds like "2 pies are" when you say it out loud! Or think "Circumference = 2 × π × radius" - you need 2 radii to make a diameter.

What if my calculator doesn't have a π button?

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Use 3.14159 for π in your calculations. So C = 22π becomes C = 22 × 3.14159 = 69.115. Most scientific calculators have a π button though!

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