Question Video: Finding the Circumference of a Circle Given a Diameter | Nagwa Question Video: Finding the Circumference of a Circle Given a Diameter | Nagwa

# Question Video: Finding the Circumference of a Circle Given a Diameter Mathematics • Second Year of Preparatory School

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Work out the circumference of the circle, giving your answer accurate to two decimal places.

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### Video Transcript

Work out the circumference of the circle, giving your answer accurate to two decimal places.

We recall first that the circumference of a circle is the distance all the way around its edge. The formula for calculating the circumference of a circle is 𝐶 equals 𝜋𝑑, where 𝐶 represents the circumference and 𝑑 represents the circle’s diameter. Looking at the diagram we’ve been given, we can see that this line segment is a diameter of the circle because its two endpoints each lie on the circle’s edge and it passes through the center of the circle. The length of this line is six, so the value of 𝑑 is six. The circumference of the circle is therefore 𝜋 multiplied by six, which we can write as six 𝜋.

Now if we needed to give an exact answer or if we didn’t have access to a calculator, we could leave our answer in this form. But we’re asked to give our answer accurate to two decimal places. So we need to evaluate this. Because 𝜋 is an irrational number, we get an answer that is also irrational, 18.84955 continuing. Rounding to two decimal places gives 18.85.

We weren’t given any units for the diameter in the question, so we don’t have any units for the circumference. But as the circumference is a measure of length, the units will be general length units. We found that the circumference of the circle to two decimal places is 18.85.

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